diff --git a/.DS_Store b/.DS_Store
deleted file mode 100644
index cdfa6b6a..00000000
Binary files a/.DS_Store and /dev/null differ
diff --git a/CPP/.DS_Store b/CPP/.DS_Store
deleted file mode 100644
index 27ac926a..00000000
Binary files a/CPP/.DS_Store and /dev/null differ
diff --git a/CPP/Problems/.DS_Store b/CPP/Problems/.DS_Store
deleted file mode 100644
index c0de1f5d..00000000
Binary files a/CPP/Problems/.DS_Store and /dev/null differ
diff --git a/CPP/Problems/Leetcode-102-Binary-Tree-Level-Order-Traversal.cpp b/CPP/Problems/BinaryTreeLevelOrderTraversal.cpp
similarity index 92%
rename from CPP/Problems/Leetcode-102-Binary-Tree-Level-Order-Traversal.cpp
rename to CPP/Problems/BinaryTreeLevelOrderTraversal.cpp
index 6a21ccea..1101222c 100644
--- a/CPP/Problems/Leetcode-102-Binary-Tree-Level-Order-Traversal.cpp
+++ b/CPP/Problems/BinaryTreeLevelOrderTraversal.cpp
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/binary-tree-level-order-traversal/
 class Solution {
 public:
     vector<vector<int>> levelOrder(TreeNode* root) {
diff --git a/CPP/Problems/BitonicArray.cpp b/CPP/Problems/BitonicArray.cpp
index 1e3b4b6e..84c920aa 100644
--- a/CPP/Problems/BitonicArray.cpp
+++ b/CPP/Problems/BitonicArray.cpp
@@ -1,95 +1,95 @@
-// Bitonic array is an array having strictly increasing order upto an element and then having strictly
-// decreasing order. It is also called Mountain array.
+    // Bitonic array is an array having strictly increasing order upto an element and then having strictly
+    // decreasing order. It is also called Mountain array.
 
-// Program to find element in a bitonic array
-// T.C.: O(log n)
-// S.C.: O(1)
-#include <iostream>
-#include <vector>
-using namespace std;
+    // Program to find element in a bitonic array
+    // T.C.: O(log n)
+    // S.C.: O(1)
+    #include <iostream>
+    #include <vector>
+    using namespace std;
 
-int findPeakIndex (vector<int> vect, int size) { // find index of peak element
-    int lo = 0, hi = size-1;
-    int mid = lo + (hi - lo)/2;
+    int findPeakIndex (vector<int> vect, int size) { // find index of peak element
+        int lo = 0, hi = size-1;
+        int mid = lo + (hi - lo)/2;
 
-    while (lo < hi) {
-        if (mid == size-1 || vect[mid] > vect[mid+1]) {
-            hi = mid;
+        while (lo < hi) {
+            if (mid == size-1 || vect[mid] > vect[mid+1]) {
+                hi = mid;
+            }
+            else if (mid == 0 || vect[mid] > vect[mid-1]) {
+                lo = mid+1;
+            }
+            mid = lo + (hi - lo)/2;
         }
-        else if (mid == 0 || vect[mid] > vect[mid-1]) {
-            lo = mid+1;
-        }
-        mid = lo + (hi - lo)/2;
+        return lo;
     }
-    return lo;
-}
 
-int leftPart (vector<int> vect, int target, int hi) { // search element in left part
-    int lo = 0;
-    int mid = lo + (hi - lo)/2;
-    while (lo <= hi) {
-        if (vect[mid] == target) {
-            return mid;
-        }
-        else if (vect[mid] > target) {
-            hi = mid - 1;
+    int leftPart (vector<int> vect, int target, int hi) { // search element in left part
+        int lo = 0;
+        int mid = lo + (hi - lo)/2;
+        while (lo <= hi) {
+            if (vect[mid] == target) {
+                return mid;
+            }
+            else if (vect[mid] > target) {
+                hi = mid - 1;
+            }
+            else {
+                lo = mid + 1;
+            }
+            mid = lo + (hi - lo)/2;
         }
-        else {
-            lo = mid + 1;
-        }
-        mid = lo + (hi - lo)/2;
+        return -1;
     }
-    return -1;
-}
 
-int rightPart (vector<int> vect, int target, int lo) { // search element in right part
-    int hi = vect.size()-1;
-    int mid = lo + (hi - lo)/2;
-    while (lo <= hi) {
-        if (vect[mid] == target) {
-            return mid;
-        }
-        else if (vect[mid] < target) {
-            hi = mid - 1;
+    int rightPart (vector<int> vect, int target, int lo) { // search element in right part
+        int hi = vect.size()-1;
+        int mid = lo + (hi - lo)/2;
+        while (lo <= hi) {
+            if (vect[mid] == target) {
+                return mid;
+            }
+            else if (vect[mid] < target) {
+                hi = mid - 1;
+            }
+            else {
+                lo = mid + 1;
+            }
+            mid = lo + (hi - lo)/2;
         }
-        else {
-            lo = mid + 1;
-        }
-        mid = lo + (hi - lo)/2;
+        return -1;
     }
-    return -1;
-}
 
-int findElement(vector<int> vect, int size, int target) {
-    // DRIVER CODE
-    // find peak of array
-    int peak = findPeakIndex (vect, size);
-    // compare peak element with target
-    if (target > vect[peak]) {return -1;}
-    else if (target == vect[peak]) {return peak;}
-    // find element in increasing/decreasing sequence
-    else {
-        int leftIndex = leftPart(vect, target, peak);
-        if (leftIndex != -1) {
-            return leftIndex;
-        }
+    int findElement(vector<int> vect, int size, int target) {
+        // DRIVER CODE
+        // find peak of array
+        int peak = findPeakIndex (vect, size);
+        // compare peak element with target
+        if (target > vect[peak]) {return -1;}
+        else if (target == vect[peak]) {return peak;}
+        // find element in increasing/decreasing sequence
         else {
-            return rightPart(vect, target, peak);
+            int leftIndex = leftPart(vect, target, peak);
+            if (leftIndex != -1) {
+                return leftIndex;
+            }
+            else {
+                return rightPart(vect, target, peak);
+            }
         }
+        return 0;
     }
-    return 0;
-}
 
-int main () {
-    vector<int> numvect;
-    int num, target;
-    cin>>num;
-    cin>>target;
-    for (int i = 0; i < num; i++) {
-        int temp;
-        cin>>temp;
-        numvect.push_back(temp);
+    int main () {
+        vector<int> numvect;
+        int num, target;
+        cin>>num;
+        cin>>target;
+        for (int i = 0; i < num; i++) {
+            int temp;
+            cin>>temp;
+            numvect.push_back(temp);
+        }
+        cout<<findElement(numvect, num, target);
+        return 0;
     }
-    cout<<findElement(numvect, num, target);
-    return 0;
-}
diff --git a/CPP/Problems/Leetcode-11-Container-With-Most-Water.cpp b/CPP/Problems/Container With Most Water.cpp
similarity index 86%
rename from CPP/Problems/Leetcode-11-Container-With-Most-Water.cpp
rename to CPP/Problems/Container With Most Water.cpp
index 6d516141..497442b4 100644
--- a/CPP/Problems/Leetcode-11-Container-With-Most-Water.cpp
+++ b/CPP/Problems/Container With Most Water.cpp	
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/container-with-most-water/
 class Solution {
 public:
     int maxArea(vector<int>& height) {
diff --git a/CPP/Problems/Leetcode-740-Delete-And-Earn.cpp b/CPP/Problems/Delete_and_Earn.cpp
similarity index 90%
rename from CPP/Problems/Leetcode-740-Delete-And-Earn.cpp
rename to CPP/Problems/Delete_and_Earn.cpp
index e6b523f5..96b1d5c7 100644
--- a/CPP/Problems/Leetcode-740-Delete-And-Earn.cpp
+++ b/CPP/Problems/Delete_and_Earn.cpp
@@ -1,4 +1,6 @@
+// Question Link
 // https://leetcode.com/problems/delete-and-earn/
+// ----------------------------------------------
 class Solution {
 public:
     int deleteAndEarn(vector<int>& nums) {
diff --git a/CPP/Problems/Find First and Last Position of Element in Sorted Array.cpp b/CPP/Problems/Find First and Last Position of Element in Sorted Array.cpp
new file mode 100644
index 00000000..8d00eff3
--- /dev/null
+++ b/CPP/Problems/Find First and Last Position of Element in Sorted Array.cpp	
@@ -0,0 +1,21 @@
+class Solution {
+public:
+    vector<int> searchRange(vector<int>& nums, int target) {
+        vector<int>ans;
+     auto low=lower_bound(nums.begin(),nums.end(),target);
+        auto upp=upper_bound(nums.begin(),nums.end(),target);
+        if(low==nums.end()|| *low!=target )
+        {
+            ans.push_back(-1);
+              ans.push_back(-1);
+        }
+        else
+        {
+            int start=low-nums.begin();
+            int end=upp-nums.begin()-1;
+            ans.push_back(start);
+             ans.push_back(end);
+        }
+        return ans;
+    }
+};
diff --git a/CPP/Problems/Leetcode-1346-Check-If-N-and-Its-Double-Exist.cpp b/CPP/Problems/Leetcode-1346-Check-If-N-and-Its-Double-Exist.cpp
deleted file mode 100644
index de7313bd..00000000
--- a/CPP/Problems/Leetcode-1346-Check-If-N-and-Its-Double-Exist.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-// https://leetcode.com/problems/check-if-n-and-its-double-exist/
-class Solution {
-public:
-    bool checkIfExist(vector<int>& arr) {
-        for (int i = 0; i < arr.size(); i++) {
-            for (int j = 0; j < arr.size(); j++) {
-                if (i!=j) {
-                    if (arr[i] == 2*arr[j])
-                        return true; 
-                }
-            }
-        }
-        return false; 
-    }
-};
\ No newline at end of file
diff --git a/CPP/Problems/Leetcode-1351-Count-Negative-Numbers-in-a-Sorted-Matrix.cpp b/CPP/Problems/Leetcode-1351-Count-Negative-Numbers-in-a-Sorted-Matrix.cpp
deleted file mode 100644
index 4054ec1b..00000000
--- a/CPP/Problems/Leetcode-1351-Count-Negative-Numbers-in-a-Sorted-Matrix.cpp
+++ /dev/null
@@ -1,17 +0,0 @@
-// https://leetcode.com/problems/count-negative-numbers-in-a-sorted-matrix/
-class Solution {
-public:
-    int countNegatives(vector<vector<int>>& grid) {
-        int count = 0; 
-
-        for (int row = 0; row < grid.size(); row++) {
-            for (int col = grid[row].size()-1; col >= 0; col--) {
-                if (grid[row][col] < 0) 
-                    count++; 
-                else 
-                    break; 
-            }
-        }
-        return count; 
-    }
-};
\ No newline at end of file
diff --git a/CPP/Problems/Leetcode-1572-Matrix-Diagonal-Sum.cpp b/CPP/Problems/Leetcode-1572-Matrix-Diagonal-Sum.cpp
deleted file mode 100644
index de887a0d..00000000
--- a/CPP/Problems/Leetcode-1572-Matrix-Diagonal-Sum.cpp
+++ /dev/null
@@ -1,23 +0,0 @@
-// https://leetcode.com/problems/matrix-diagonal-sum/
-class Solution {
-public:
-    int diagonalSum(vector<vector<int>>& mat) {
-        int rc = 0; 
-        int TotalSum = 0; 
-        // Primary Diagonal
-        while (rc < mat.size()) {
-            TotalSum += mat[rc][rc];
-            rc++; 
-        }
-        // Secondary Diagonal
-        int r = mat.size()-1, c = 0; 
-        while (r >= 0 && c < mat.size()) {
-            TotalSum += mat[r][c];
-            r--; 
-            c++;    
-        }
-        if (mat.size() & 1) 
-            return TotalSum - (mat[mat.size()/2][mat.size()/2]);
-        return TotalSum; 
-    }
-};
\ No newline at end of file
diff --git a/CPP/Problems/Leetcode-231-Power-of-Two.cpp b/CPP/Problems/Leetcode-231-Power-of-Two.cpp
deleted file mode 100644
index 7a074138..00000000
--- a/CPP/Problems/Leetcode-231-Power-of-Two.cpp
+++ /dev/null
@@ -1,7 +0,0 @@
-// https://leetcode.com/problems/power-of-two/
-class Solution {
-public:
-    bool isPowerOfTwo(int x) {
-        return x && (!(x&(x-1)));
-    }
-};
\ No newline at end of file
diff --git a/CPP/Problems/Leetcode-287-Find-the-Duplicate-Number.cpp b/CPP/Problems/Leetcode-287-Find-the-Duplicate-Number.cpp
deleted file mode 100644
index b6b30564..00000000
--- a/CPP/Problems/Leetcode-287-Find-the-Duplicate-Number.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-// https://leetcode.com/problems/find-the-duplicate-number/
-class Solution {
-public:
-    int findDuplicate(vector<int>& nums) {
-        
-        // first thing that comes to my mind is using the set - with O(N) space
-        // using two for loop (N^2) 
-        // using another array of same size and updating the value if every times
-        //element is there
-        int slow=0; 
-        int fast=0; 
-        
-        do {
-            slow=nums[slow]; 
-            fast=nums[nums[fast]]; 
-            
-        }while (slow !=fast); 
-        
-        int slow2=0; 
-        
-        while (slow2!=slow){
-            slow2=nums[slow2]; 
-            slow=nums[slow]; 
-        }
-        
-        return slow; 
-        
-    }
-};
-
diff --git a/CPP/Problems/Leetcode-34-find-first-and-last-position-of-element-in-sorted-array.cpp b/CPP/Problems/Leetcode-34-find-first-and-last-position-of-element-in-sorted-array.cpp
index a98ff0cd..6ebcb4e2 100644
--- a/CPP/Problems/Leetcode-34-find-first-and-last-position-of-element-in-sorted-array.cpp
+++ b/CPP/Problems/Leetcode-34-find-first-and-last-position-of-element-in-sorted-array.cpp
@@ -1,22 +1,36 @@
-// https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/
 class Solution {
 public:
     vector<int> searchRange(vector<int>& nums, int target) {
-        vector<int>ans;
-     auto low=lower_bound(nums.begin(),nums.end(),target);
-        auto upp=upper_bound(nums.begin(),nums.end(),target);
-        if(low==nums.end()|| *low!=target )
-        {
-            ans.push_back(-1);
-              ans.push_back(-1);
+        int n=nums.size();
+        int l=0,r=n-1;
+        int p1=-1,p2=-1;
+        while(l<=r){
+            int mid=l+(r-l)/2;
+            if(nums[mid]==target){
+                p1=mid;
+                r=mid-1;
+            }
+            else if(nums[mid]>target){
+                r=mid-1;
+            }
+            else
+                l=mid+1;
         }
-        else
-        {
-            int start=low-nums.begin();
-            int end=upp-nums.begin()-1;
-            ans.push_back(start);
-             ans.push_back(end);
+        l=0,r=n-1;
+        while(l<=r){
+            int mid=l+(r-l)/2;
+            if(nums[mid]>=target+1){
+                r=mid-1;
+            }
+            else{
+                
+                l=mid+1;
+            }
+                
         }
-        return ans;
+        p2=l;
+        if(p1!=-1)
+        return {p1,p2-1};
+        return {-1,-1};
     }
 };
diff --git a/CPP/Problems/Leetcode-43-Multiply-Strings.cpp b/CPP/Problems/Leetcode-43-Multiply-Strings.cpp
deleted file mode 100644
index 6b572c10..00000000
--- a/CPP/Problems/Leetcode-43-Multiply-Strings.cpp
+++ /dev/null
@@ -1,8 +0,0 @@
-// https://leetcode.com/problems/multiply-strings/
-class Solution {
-public:
-    string multiply(string num1, string num2) {
-        int n1 = stoi(num1), n2 = stoi(num2);
-        return to_string(n1*n2); 
-    }
-};
\ No newline at end of file
diff --git a/CPP/Problems/Leetcode-7-Reverse-Integer.cpp b/CPP/Problems/Leetcode-7-Reverse-Integer.cpp
deleted file mode 100644
index e9dfd061..00000000
--- a/CPP/Problems/Leetcode-7-Reverse-Integer.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-// https://leetcode.com/problems/reverse-integer/
-class Solution {
-public:
-   int reverse(int x) {
-      int reverse =0;
-      while (x!=0)
-      {
-         if(214748364<reverse || -214748364 > reverse)
-            return 0;
-         reverse= (reverse * 10) + x%10;
-         x/=10;
-      }
-      return reverse;
-   }
-};
diff --git a/CPP/Problems/Leetcode-674-Longest-Continuous-Increasing-Subsequence-Easy.cpp b/CPP/Problems/Longest-Continuous-Increasing-Subsequence-Easy.cpp
similarity index 82%
rename from CPP/Problems/Leetcode-674-Longest-Continuous-Increasing-Subsequence-Easy.cpp
rename to CPP/Problems/Longest-Continuous-Increasing-Subsequence-Easy.cpp
index 6676d1eb..755ca9e8 100644
--- a/CPP/Problems/Leetcode-674-Longest-Continuous-Increasing-Subsequence-Easy.cpp
+++ b/CPP/Problems/Longest-Continuous-Increasing-Subsequence-Easy.cpp
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/longest-continuous-increasing-subsequence/
 class Solution {
 public:
     int findLengthOfLCIS(vector<int>& nums) {
diff --git a/CPP/Problems/Leetcode-152-Maximum-Product-Subarray.cpp b/CPP/Problems/MaximumProductSubarray.cpp
similarity index 89%
rename from CPP/Problems/Leetcode-152-Maximum-Product-Subarray.cpp
rename to CPP/Problems/MaximumProductSubarray.cpp
index c3f97ea9..5a5c56a9 100644
--- a/CPP/Problems/Leetcode-152-Maximum-Product-Subarray.cpp
+++ b/CPP/Problems/MaximumProductSubarray.cpp
@@ -1,4 +1,7 @@
+// Question Link
 // https://leetcode.com/problems/maximum-product-subarray/
+// ----------------------------------------------
+
 class Solution {
 public:
     int maxProduct(vector<int>& nums) {
diff --git a/CPP/Problems/Leetcode-4-Median-of-Two-Sorted-Arrays.cpp b/CPP/Problems/Median of Two Sorted Arrays.cpp
similarity index 93%
rename from CPP/Problems/Leetcode-4-Median-of-Two-Sorted-Arrays.cpp
rename to CPP/Problems/Median of Two Sorted Arrays.cpp
index b83e8dcf..fb2772ea 100644
--- a/CPP/Problems/Leetcode-4-Median-of-Two-Sorted-Arrays.cpp
+++ b/CPP/Problems/Median of Two Sorted Arrays.cpp	
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/median-of-two-sorted-arrays/
 class Solution {
 public:
     double findMedianSortedArrays(vector<int>& nums1, vector<int>& nums2) {
diff --git a/CPP/Problems/Leetcode-1155-Number-of-dice-rolls-with-targe-sum.cpp b/CPP/Problems/Number of Dice Rolls With Target Sum.cpp
similarity index 90%
rename from CPP/Problems/Leetcode-1155-Number-of-dice-rolls-with-targe-sum.cpp
rename to CPP/Problems/Number of Dice Rolls With Target Sum.cpp
index 45527c8a..fc091137 100644
--- a/CPP/Problems/Leetcode-1155-Number-of-dice-rolls-with-targe-sum.cpp
+++ b/CPP/Problems/Number of Dice Rolls With Target Sum.cpp	
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/number-of-dice-rolls-with-target-sum/
 class Solution {
 public:
     
diff --git a/CPP/Problems/Leetcode-9-Palindrome-Number.cpp b/CPP/Problems/Palindrome Number.cpp
similarity index 89%
rename from CPP/Problems/Leetcode-9-Palindrome-Number.cpp
rename to CPP/Problems/Palindrome Number.cpp
index 27605362..6b4ba480 100644
--- a/CPP/Problems/Leetcode-9-Palindrome-Number.cpp
+++ b/CPP/Problems/Palindrome Number.cpp	
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/palindrome-number/
 class Solution {
 public:
     bool isPalindrome(int x) {
diff --git a/CPP/Problems/Reverse Integer.cpp b/CPP/Problems/Reverse Integer.cpp
new file mode 100644
index 00000000..f390d5de
--- /dev/null
+++ b/CPP/Problems/Reverse Integer.cpp	
@@ -0,0 +1,17 @@
+class Solution {
+public:
+   int reverse(int x) {
+int reverse =0;
+while (x!=0)
+{
+if(214748364<reverse || -214748364 > reverse)
+return 0;
+reverse= (reverse * 10) + x%10;
+x/=10;
+}
+return reverse;
+}
+        
+        
+    
+};
diff --git a/CPP/Problems/Leetcode-13-Roman-to-Integer.cpp b/CPP/Problems/Roman to Integer.cpp
similarity index 90%
rename from CPP/Problems/Leetcode-13-Roman-to-Integer.cpp
rename to CPP/Problems/Roman to Integer.cpp
index d9d179f7..bb2a56ad 100644
--- a/CPP/Problems/Leetcode-13-Roman-to-Integer.cpp
+++ b/CPP/Problems/Roman to Integer.cpp	
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/roman-to-integer/
 class Solution {
 public:
     int romanToInt(string s) {
diff --git a/CPP/Problems/Leetcode-8-String-to-Integer-(atoi).cpp b/CPP/Problems/String to Integer (atoi).cpp
similarity index 95%
rename from CPP/Problems/Leetcode-8-String-to-Integer-(atoi).cpp
rename to CPP/Problems/String to Integer (atoi).cpp
index daf1e6a1..53cd345d 100644
--- a/CPP/Problems/Leetcode-8-String-to-Integer-(atoi).cpp
+++ b/CPP/Problems/String to Integer (atoi).cpp	
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/string-to-integer-atoi/
 class Solution {
 public:
   int myAtoi(string s) {
diff --git a/CPP/Problems/Leetcode-2-Add-Two-Numbers.cpp b/CPP/Problems/add-two-numbers.cpp
similarity index 96%
rename from CPP/Problems/Leetcode-2-Add-Two-Numbers.cpp
rename to CPP/Problems/add-two-numbers.cpp
index 80c433a9..af90a79c 100644
--- a/CPP/Problems/Leetcode-2-Add-Two-Numbers.cpp
+++ b/CPP/Problems/add-two-numbers.cpp
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/add-two-numbers/
 /**
  * Definition for singly-linked list.
  * struct ListNode {
diff --git a/CPP/Problems/Leetcode-2425-Bitwise-XOR-Of-All-Pairings.cpp b/CPP/Problems/biwise_xor_pairing.cpp
similarity index 89%
rename from CPP/Problems/Leetcode-2425-Bitwise-XOR-Of-All-Pairings.cpp
rename to CPP/Problems/biwise_xor_pairing.cpp
index 3bcb7b30..c15876e5 100644
--- a/CPP/Problems/Leetcode-2425-Bitwise-XOR-Of-All-Pairings.cpp
+++ b/CPP/Problems/biwise_xor_pairing.cpp
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/bitwise-xor-of-all-pairings/
 class Solution {
 public:
     int xorAllNums(vector<int>& nums1, vector<int>& nums2) {
diff --git a/CPP/Problems/Leetcode-1232-Check-If-It-Is-A-Straight-Line.cpp b/CPP/Problems/check-if-it-is-a-straight-line.cpp
similarity index 100%
rename from CPP/Problems/Leetcode-1232-Check-If-It-Is-A-Straight-Line.cpp
rename to CPP/Problems/check-if-it-is-a-straight-line.cpp
diff --git a/CPP/Problems/findTheDuplicateNumber.cpp b/CPP/Problems/findTheDuplicateNumber.cpp
new file mode 100644
index 00000000..e37f2d7c
--- /dev/null
+++ b/CPP/Problems/findTheDuplicateNumber.cpp
@@ -0,0 +1,64 @@
+/* Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.
+
+There is only one repeated number in nums, return this repeated number.
+
+You must solve the problem without modifying the array nums and uses only constant extra space.
+
+ 
+
+Example 1:
+
+Input: nums = [1,3,4,2,2]
+Output: 2
+Example 2:
+
+Input: nums = [3,1,3,4,2]
+Output: 3
+ 
+
+Constraints:
+
+1 <= n <= 105
+nums.length == n + 1
+1 <= nums[i] <= n
+All the integers in nums appear only once except for precisely one integer which appears two or more times.
+ 
+
+Follow up:
+
+How can we prove that at least one duplicate number must exist in nums?
+Can you solve the problem in linear runtime complexity?
+
+
+
+Solution:*/
+
+class Solution {
+public:
+    int findDuplicate(vector<int>& nums) {
+        
+        // first thing that comes to my mind is using the set - with O(N) space
+        // using two for loop (N^2) 
+        // using another array of same size and updating the value if every times
+        //element is there
+        int slow=0; 
+        int fast=0; 
+        
+        do {
+            slow=nums[slow]; 
+            fast=nums[nums[fast]]; 
+            
+        }while (slow !=fast); 
+        
+        int slow2=0; 
+        
+        while (slow2!=slow){
+            slow2=nums[slow2]; 
+            slow=nums[slow]; 
+        }
+        
+        return slow; 
+        
+    }
+};
+
diff --git a/CPP/Problems/Leetcode-53-Maximum-Subarray.cpp b/CPP/Problems/maximum-subarray.cpp
similarity index 100%
rename from CPP/Problems/Leetcode-53-Maximum-Subarray.cpp
rename to CPP/Problems/maximum-subarray.cpp
diff --git a/CPP/Problems/Leetcode-88-Merge-Sorted-Arrays.cpp b/CPP/Problems/merge-sorted-arrays.cpp
similarity index 89%
rename from CPP/Problems/Leetcode-88-Merge-Sorted-Arrays.cpp
rename to CPP/Problems/merge-sorted-arrays.cpp
index 1f8b1778..584fb99c 100644
--- a/CPP/Problems/Leetcode-88-Merge-Sorted-Arrays.cpp
+++ b/CPP/Problems/merge-sorted-arrays.cpp
@@ -1,8 +1,7 @@
-// https://leetcode.com/problems/merge-sorted-array/
 class Solution {
 public:
     void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
-        int h=m;
+         int h=m;
         int j=(m+n)-1;
         int i=0;
         int k=0;
diff --git a/CPP/Problems/Leetcode-283-Move-Zeroes.cpp b/CPP/Problems/move-zeroes.cpp
similarity index 89%
rename from CPP/Problems/Leetcode-283-Move-Zeroes.cpp
rename to CPP/Problems/move-zeroes.cpp
index e4722a2f..68e67964 100644
--- a/CPP/Problems/Leetcode-283-Move-Zeroes.cpp
+++ b/CPP/Problems/move-zeroes.cpp
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/move-zeroes/
 class Solution {
 public:
     void moveZeroes(vector<int>& nums) {
diff --git a/CPP/Problems/Leetcode-50-Pow(x,n).cpp b/CPP/Problems/pow(x,n).cpp
similarity index 89%
rename from CPP/Problems/Leetcode-50-Pow(x,n).cpp
rename to CPP/Problems/pow(x,n).cpp
index 0b497a84..c844629b 100644
--- a/CPP/Problems/Leetcode-50-Pow(x,n).cpp
+++ b/CPP/Problems/pow(x,n).cpp
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/powx-n/
 class Solution {
 public:
   //binary exponentiation
diff --git a/CPP/Problems/queries-on-number-of-points-inside-circle.cpp b/CPP/Problems/queries-on-number-of-points-inside-circle.cpp
new file mode 100644
index 00000000..78a3fda4
--- /dev/null
+++ b/CPP/Problems/queries-on-number-of-points-inside-circle.cpp
@@ -0,0 +1,25 @@
+class Solution {
+public:
+    bool checkStraightLine(vector<vector<int>>& coordinates) {
+        bool flag=true;
+        
+        int x1=coordinates[0][0];
+        int y1=coordinates[0][1];
+        int x2=coordinates[1][0];
+        int y2=coordinates[1][1];
+        int m1=y2-y1;
+        int m2=x2-x1;
+        int curdx=0;
+        int curdy=0;
+       for(int i=2;i<coordinates.size();i++)
+       {
+           curdx=coordinates[i][0]-coordinates[i-1][0];
+           curdy=coordinates[i][1]-coordinates[i-1][1];
+           
+           if(curdx*m1!=curdy*m2)
+               return false;
+       }
+        return true;
+      
+    }
+};
diff --git a/CPP/Problems/Leetcode-1-Two-Sum.cpp b/CPP/Problems/two-sum.cpp
similarity index 92%
rename from CPP/Problems/Leetcode-1-Two-Sum.cpp
rename to CPP/Problems/two-sum.cpp
index a3952559..da08263f 100644
--- a/CPP/Problems/Leetcode-1-Two-Sum.cpp
+++ b/CPP/Problems/two-sum.cpp
@@ -1,4 +1,3 @@
-// https://leetcode.com/problems/two-sum/
 class Solution {
 public:
     vector<int> twoSum(vector<int>& nums, int target) {
diff --git a/CPP/Problems/Leetcode-941-Valid-Mountain-Array.cpp b/CPP/Problems/valid-mountain-array.cpp
similarity index 88%
rename from CPP/Problems/Leetcode-941-Valid-Mountain-Array.cpp
rename to CPP/Problems/valid-mountain-array.cpp
index 301f38d6..936c9fb5 100644
--- a/CPP/Problems/Leetcode-941-Valid-Mountain-Array.cpp
+++ b/CPP/Problems/valid-mountain-array.cpp
@@ -1,4 +1,4 @@
-// https://leetcode.com/problems/valid-mountain-array/
+
 class Solution {
 public:
     bool validMountainArray(vector<int>& A) {