# Next Greater Element in C++

C++Server Side ProgrammingProgramming

The next greater element is the element that is first greater element after it. Let's see an example.

arr = [4, 5, 3, 2, 1]

The next greater element for 4 is 5 and the next greater element for elements 3, 2, 1 is -1 as there is no greater element after them.

## Algorithm

• Initialise the array with random numbers.

• Initialise a stack.

• Add first element to the stack.

• Iterate through the element of the array.

• If the stack is empty, add the current element to the stack.

• While the current element is greater than the top element of the stack.

• Print the top element with the next greater element as current element.

• Pop the top element.

• Add the element to the stack.

• While stack is not empty.

• Print the elements with next greater element as -1.

## Implementation

Following is the implementation of the above algorithm in C++

#include <bits/stdc++.h>
using namespace std;
void nextGreaterElements(int arr[], int n) {
stack<int> s;
s.push(arr);
for (int i = 1; i < n; i++) {
if (s.empty()) {
s.push(arr[i]);
continue;
}
while (!s.empty() && s.top() < arr[i]) {
cout << s.top() << " -> " << arr[i] << endl;
s.pop();
}
s.push(arr[i]);
}
while (!s.empty()) {
cout << s.top() << " -> " << -1 << endl;
s.pop();
}
}
int main() {
int arr[] = { 1, 2, 3, 4, 5 };
int n = 5;
nextGreaterElements(arr, n);
return 0;
}

## Output

If you run the above code, then you will get the following result.

1 -> 2
2 -> 3
3 -> 4
4 -> 5
5 -> -1