Merge pull request #2101 from shreyash3087/add/leetcode-917

Docs: Added Solutions to Leetcode 917

Author: ajay-dhangar

dsa-problems/leetcode-problems/0900-0999.md

@@ -117,7 +117,7 @@ export const problems = [
         problemName: "917. Reverse Only Letters",
         difficulty: "Easy",
         leetCodeLink: "https://leetcode.com/problems/reverse-only-letters",
-        solutionLink: "#"
+        solutionLink: "/dsa-solutions/lc-solutions/0900-0999/reverse-only-letters"
     },
     {
         problemName: "918. Maximum Sum Circular Subarray",

dsa-solutions/lc-solutions/0900-0999/0917-reverse-only-letters.md

@@ -0,0 +1,237 @@
+---
+id: reverse-only-letters
+title: Reverse Only Letters
+sidebar_label: 0917 - Reverse Only Letters
+tags:
+  - Two Pointers
+  - String
+  - Stack
+description: "This is a solution to the Reverse Only Letters problem on LeetCode."
+---
+
+## Problem Description
+
+Given a string `s`, reverse the string according to the following rules:
+
+- All the characters that are not English letters remain in the same position.
+- All the English letters (lowercase or uppercase) should be reversed.
+
+Return `s` after reversing it.
+
+### Examples
+
+**Example 1:**
+
+```
+Input: s = "ab-cd"
+Output: "dc-ba"
+```
+**Example 2:**
+
+```
+Input: s = "a-bC-dEf-ghIj"
+Output: "j-Ih-gfE-dCba"
+```
+
+### Constraints
+
+- $1 \leq s.length \leq 100$
+- `s` consists of characters with ASCII values in the range `[33, 122]`.
+- `s` does not contain `'\"'` or `'\\'`.
+
+## Solution for Reverse Only Letters
+
+## Approach: Stack of Letters
+### Intuition and Algorithm
+
+Collect the letters of `S` separately into a stack, so that popping the stack reverses the letters. (Alternatively, we could have collected the letters into an array and reversed the array.)
+
+Then, when writing the characters of `S`, any time we need a letter, we use the one we have prepared instead.
+
+### Code in Different Languages
+
+<Tabs>
+<TabItem value="cpp" label="C++">
+  <SolutionAuthor name="@Shreyash3087"/>
+
+```cpp
+class Solution {
+public:
+    string reverseOnlyLetters(string S) {
+        stack<char> letters;
+        for (char c : S)
+            if (isalpha(c))
+                letters.push(c);
+
+        string ans;
+        for (char c : S) {
+            if (isalpha(c))
+                ans += letters.top(), letters.pop();
+            else
+                ans += c;
+        }
+
+        return ans;
+    }
+};
+
+```
+</TabItem>
+<TabItem value="java" label="Java">
+  <SolutionAuthor name="@Shreyash3087"/>
+
+```java
+class Solution {
+    public String reverseOnlyLetters(String S) {
+        Stack<Character> letters = new Stack();
+        for (char c: S.toCharArray())
+            if (Character.isLetter(c))
+                letters.push(c);
+
+        StringBuilder ans = new StringBuilder();
+        for (char c: S.toCharArray()) {
+            if (Character.isLetter(c))
+                ans.append(letters.pop());
+            else
+                ans.append(c);
+        }
+
+        return ans.toString();
+    }
+}
+```
+
+</TabItem>
+<TabItem value="python" label="Python">
+  <SolutionAuthor name="@Shreyash3087"/>
+
+```python
+class Solution(object):
+    def reverseOnlyLetters(self, S):
+        letters = [c for c in S if c.isalpha()]
+        ans = []
+        for c in S:
+            if c.isalpha():
+                ans.append(letters.pop())
+            else:
+                ans.append(c)
+        return "".join(ans)
+```
+</TabItem>
+</Tabs>
+
+### Complexity Analysis
+
+#### Time Complexity: $O(N)$
+
+> **Reason**: where `N` is the length of `S`.
+
+#### Space Complexity: $O(N)$
+
+## Approach: Reverse Pointer
+### Intuition
+
+Write the characters of `S` one by one. When we encounter a letter, we want to write the next letter that occurs if we iterated through the string backwards.
+
+So we do just that: keep track of a pointer `j` that iterates through the string backwards. When we need to write a letter, we use it.
+
+### Code in Different Languages
+
+<Tabs>
+<TabItem value="cpp" label="C++">
+  <SolutionAuthor name="@Shreyash3087"/>
+
+```cpp
+#include <string>
+#include <cctype>
+#include <sstream>
+
+class Solution {
+public:
+    std::string reverseOnlyLetters(std::string S) {
+        std::stringstream ans;
+        int j = S.length() - 1;
+        for (int i = 0; i < S.length(); ++i) {
+            if (std::isalpha(S[i])) {
+                while (!std::isalpha(S[j]))
+                    j--;
+                ans << S[j--];
+            } else {
+                ans << S[i];
+            }
+        }
+
+        return ans.str();
+    }
+};
+
+```
+</TabItem>
+<TabItem value="java" label="Java">
+  <SolutionAuthor name="@Shreyash3087"/>
+
+```java
+class Solution {
+    public String reverseOnlyLetters(String S) {
+        StringBuilder ans = new StringBuilder();
+        int j = S.length() - 1;
+        for (int i = 0; i < S.length(); ++i) {
+            if (Character.isLetter(S.charAt(i))) {
+                while (!Character.isLetter(S.charAt(j)))
+                    j--;
+                ans.append(S.charAt(j--));
+            } else {
+                ans.append(S.charAt(i));
+            }
+        }
+
+        return ans.toString();
+    }
+}
+```
+
+</TabItem>
+<TabItem value="python" label="Python">
+  <SolutionAuthor name="@Shreyash3087"/>
+
+```python
+class Solution(object):
+    def reverseOnlyLetters(self, S):
+        ans = []
+        j = len(ans) - 1
+        for i, x in enumerate(S):
+            if x.isalpha():
+                while not S[j].isalpha():
+                    j -= 1
+                ans.append(S[j])
+                j -= 1
+            else:
+                ans.append(x)
+        
+        return "".join(ans)
+```
+</TabItem>
+</Tabs>
+
+### Complexity Analysis
+
+#### Time Complexity: $O(N)$
+
+> **Reason**: where `N` is the length of `S`.
+
+#### Space Complexity: $O(N)$
+
+## Video Solution 
+
+<LiteYouTubeEmbed
+    id="M2TwbZCpJpw"
+    params="autoplay=1&autohide=1&showinfo=0&rel=0"
+    title="LeetCode Reverse Only Letters Solution Explained - Java"
+    poster="hqdefault"
+    webp />
+
+## References
+
+- **LeetCode Problem**: [Reverse Only Letters](https://leetcode.com/problems/reverse-only-letters/description/)
+
+- **Solution Link**: [Reverse Only Letters](https://leetcode.com/problems/reverse-only-letters/solutions/)