Next Greater Element in Array

Given an array arr[] of integers, determine the Next Greater Element (NGE) for every element in the array, maintaining the order of appearance.

• The Next Greater Element for an element x is defined as the first element to the right of x in the array that is strictly greater than x.
• If no such element exists for an element, its Next Greater Element is -1.

Examples: 

Input: arr[] = [1, 3, 2, 4]
Output: [3, 4, 4, -1]
Explanation: The next larger element to 1 is 3, 3 is 4, 2 is 4 and for 4, since it doesn't exist, it is -1.

Input: arr[] = [6, 8, 0, 1, 3]
Output: [8, -1, 1, 3, -1]
Explanation: The next larger element to 6 is 8, for 8 there is no larger elements hence it is -1, for 0 it is 1 , for 1 it is 3 and then for 3 there is no larger element on right and hence -1.

[Naive Approach] Using Nested Loops - O(n²) Time and O(1) Space

The idea is to look at all the elements to its right and check if there's a larger element for each element in the array. If we find one, we store it as the next greater element. If no greater element is found, we store -1. This is done using two nested loops: the outer loop goes through each element, and the inner loop searches the rest of the array for a greater element.

#include <iostream>
#include <vector>
using namespace std;

vector<int> nextLargerElement(vector<int> &arr) {
    int n = arr.size();
    vector<int> res(n, -1);

    // iterate through each element in the array
    for (int i = 0; i < n; i++) {

        // check for the next greater element
        // in the rest of the array
        for (int j = i + 1; j < n; j++) {
            if (arr[j] > arr[i]) {
                res[i] = arr[j];
                break;
            }
        }
    }

    return res;
}

int main() {

    vector<int> arr = {6, 8, 0, 1, 3};
    vector<int> res = nextLargerElement(arr);
    for (int x : res) {
        cout << x << " ";
    }

    return 0;
}

import java.util.ArrayList;

class GfG {

    static ArrayList<Integer> nextLargerElement(int[] arr) {
        int n = arr.length;
        ArrayList<Integer> res = new ArrayList<>();

        // initialize res with -1 for all elements
        for (int i = 0; i < n; i++) {
            res.add(-1);
        }

        // iterate through each element in the array
        for (int i = 0; i < n; i++) {

            // check for the next greater element
            // in the rest of the array
            for (int j = i + 1; j < n; j++) {
                if (arr[j] > arr[i]) {
                    res.set(i, arr[j]);
                    break;
                }
            }
        }

        return res;
    }

    public static void main(String[] args) {

        int[] arr = { 6, 8, 0, 1, 3 };
        ArrayList<Integer> res = nextLargerElement(arr);
        for (int x : res) {
            System.out.print(x + " ");
        }
    }
}

def nextLargerElement(arr):
    n = len(arr)
    res = [-1] * n  

    # Iterate through each element in the array
    for i in range(n):

        # Check for the next greater element 
        # in the rest of the array
        for j in range(i + 1, n):
            if arr[j] > arr[i]:
                res[i] = arr[j]
                break

    return res

if __name__ == "__main__":
    arr = [6, 8, 0, 1, 3]

    res = nextLargerElement(arr)
    print(" ".join(map(str, res)))

using System;
using System.Collections.Generic;

class GfG {

    static List<int> nextLargerElement(int[] arr) {
        int n = arr.Length;
        List<int> res = new List<int>(new int[n]);

        // Initialize res with -1 for all elements
        for (int i = 0; i < n; i++) {
            res[i] = -1;
        }

        // Iterate through each element in the array
        for (int i = 0; i < n; i++) {

            // Check for the next greater element
            // in the rest of the array
            for (int j = i + 1; j < n; j++) {
                if (arr[j] > arr[i]) {
                    res[i] = arr[j];
                    break;
                }
            }
        }

        return res;
    }

    static void Main(string[] args) {
        int[] arr = { 6, 8, 0, 1, 3 };
        List<int> res = nextLargerElement(arr);
        foreach(int x in res) { Console.Write(x + " "); }
    }
}

function nextLargerElement(arr) {

    let