Array leaders from gfg is added

dsa-solutions/gfg-solutions/Easy problems/Array-Leaders.md

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+---
+id: array-leaders
+title: Array Leaders
+sidebar_label: Array-Leaders
+tags:
+  - Array
+  - Data Structure
+description: "This tutorial covers the solution to the Array Leaders problem from the GeeksforGeeks website."
+---
+## Problem Description
+
+Given an array `arr` of `n` positive integers, your task is to find all the leaders in the array. An element of the array is considered a leader if it is greater than all the elements on its right side or if it is equal to the maximum element on its right side. The rightmost element is always a leader.
+
+## Examples
+
+**Example 1:**
+
+```
+Input:
+arr = [16, 17, 4, 3, 5, 2]
+Output: 17, 5, 2
+Explanation: The leaders are 17, 5, and 2.
+```
+
+**Example 2:**
+
+```
+Input:
+arr = [1, 2, 3, 4, 0]
+Output: 4, 0
+Explanation: The leaders are 4 and 0.
+```
+
+## Your Task
+
+You don't need to read input or print anything. Your task is to complete the function `leaders()` which takes the array `arr[]` and its size `n` as input parameters and returns a list of integers containing the leaders in the array.
+
+Expected Time Complexity: $O(n)$
+
+Expected Auxiliary Space: $O(n)$
+
+## Constraints
+
+* `1 ≤ n ≤ 10^7`
+* `0 ≤ arr[i] ≤ 10^7`
+
+## Problem Explanation
+
+The task is to find all the leaders in the array, where a leader is an element that is greater than or equal to all the elements to its right. The rightmost element is always a leader.
+
+## Code Implementation
+
+<Tabs>
+  <TabItem value="Python" label="Python" default>
+  <SolutionAuthor name="@Ishitamukherjee2004"/>
+
+  ```python
+  class Solution:
+      def leaders(self, arr, n):
+          leaders = []
+          max_from_right = arr[-1]
+          leaders.append(max_from_right)
+
+          for i in range(n-2, -1, -1):
+              if arr[i] >= max_from_right:
+                  leaders.append(arr[i])
+                  max_from_right = arr[i]
+
+          return leaders[::-1]
+
+  # Example usage
+  if __name__ == "__main__":
+      solution = Solution()
+      arr = [16, 17, 4, 3, 5, 2]
+      print(solution.leaders(arr, len(arr)))  # Expected output: [17, 5, 2]
+  ```
+
+  </TabItem>
+  <TabItem value="C++" label="C++">
+  <SolutionAuthor name="@Ishitamukherjee2004"/>
+
+  ```cpp
+  //{ Driver Code Starts
+  #include <bits/stdc++.h>
+  using namespace std;
+
+  // } Driver Code Ends
+  class Solution {
+  public:
+      vector<int> leaders(int n, int arr[]) {
+          vector<int> leaders;
+          int max_from_right = arr[n-1];
+          leaders.push_back(max_from_right);
+
+          for (int i = n-2; i >= 0; i--) {
+              if (arr[i] >= max_from_right) {
+                  leaders.push_back(arr[i]);
+                  max_from_right = arr[i];
+              }
+          }
+
+          reverse(leaders.begin(), leaders.end());
+          return leaders;
+      }
+  };
+
+  //{ Driver Code Starts.
+  int main() {
+      long long t;
+      cin >> t; // testcases
+      while (t--) {
+          long long n;
+          cin >> n; // total size of array
+
+          int arr[n];
+
+          // inserting elements in the array
+          for (long long i = 0; i < n; i++) {
+              cin >> arr[i];
+          }
+          Solution obj;
+          // calling leaders() function
+          vector<int> v = obj.leaders(n, arr);
+
+          // printing elements of the vector
+          for (auto it = v.begin(); it != v.end(); it++) {
+              cout << *it << " ";
+          }
+
+          cout << endl;
+      }
+  }
+  // } Driver Code Ends
+  ```
+
+  </TabItem>
+
+  <TabItem value="Javascript" label="Javascript" default>
+  <SolutionAuthor name="@Ishitamukherjee2004"/>
+
+  ```javascript
+  class Solution {
+  leaders(arr, n) {
+    let leaders = [];
+    let maxFromRight = arr[n - 1];
+    leaders.push(maxFromRight);
+    for (let i = n - 2; i >= 0; i--) {
+      if (arr[i] >= maxFromRight) {
+        leaders.push(arr[i]);
+        maxFromRight = arr[i];
+      }
+    }
+    return leaders.reverse();
+  }
+}
+
+  ```
+
+  </TabItem>
+
+  <TabItem value="Typescript" label="Typescript" default>
+  <SolutionAuthor name="@Ishitamukherjee2004"/>
+
+  ```typescript
+class Solution {
+  leaders(arr: number[], n: number): number[] {
+    let leaders: number[] = [];
+    let maxFromRight: number = arr[n - 1];
+    leaders.push(maxFromRight);
+    for (let i: number = n - 2; i >= 0; i--) {
+      if (arr[i] >= maxFromRight) {
+        leaders.push(arr[i]);
+        maxFromRight = arr[i];
+      }
+    }
+    return leaders.reverse();
+  }
+}
+
+
+  ```
+
+  </TabItem>
+
+  <TabItem value="Java" label="Java" default>
+  <SolutionAuthor name="@Ishitamukherjee2004"/>
+
+  ```java
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class Solution {
+  public ArrayList<Integer> leaders(ArrayList<Integer> arr, int n) {
+    ArrayList<Integer> leaders = new ArrayList<Integer>();
+    int maxFromRight = arr.get(n - 1);
+    leaders.add(maxFromRight);
+    for (int i = n - 2; i >= 0; i--) {
+      if (arr.get(i) >= maxFromRight) {
+        leaders.add(arr.get(i));
+        maxFromRight = arr.get(i);
+      }
+    }
+    Collections.reverse(leaders);
+    return leaders;
+  }
+}
+
+  ```
+
+  </TabItem>
+</Tabs>
+
+
+## Solution Logic:
+
+1. Traverse the array from right to left.
+2. Keep track of the maximum element encountered so far.
+3. If the current element is greater than or equal to the maximum element, it is a leader.
+4. Add the leader to the result list and update the maximum element.
+5. Return the result list in reverse order.
+
+## Time Complexity
+
+* The function iterates through the array once, so the time complexity is $O(n)$.
+
+## Space Complexity
+
+* The function uses additional space for the result list, so the auxiliary space complexity is $O(n)$.