Next Smaller Element Python

PROGRAM TO FIND THE NEXT SMALLER ELEMENT FOR EVERY ELEMENT

using System;

using System.Collections.Generic;

public class GFG

{

    /* prints element and NSE pair for all

    elements of arr[] of size n */

    public static void printNSE(int []arr, int n)

    {

        Stack<int> s = new Stack<int>();

          

        /* push the first element to stack */

        s.Push(arr[0]);

          

        // iterate for rest of the elements

        for (int i = 1; i < n; i++) {

  

        if (s.Count==0) {

            s.Push(arr[i]);

            continue;

        }

      

          

        /* if stack is not empty, then

        pop an element from stack.

        If the popped element is greater

        than next, then

        a) print the pair

        b) keep popping while elements are

        greater and stack is not empty */

    while (s.Count !=0 && s.Peek() > arr[i]) {

            Console.WriteLine(s.Peek() + " --> " + arr[i]);

            s.Pop();

        }

          

        /* push next to stack so that we can find

        next smaller for it */

        s.Push(arr[i]);

        }

          

        /* After iterating over the loop, the remaining

        elements in stack do not have the next smaller

        element, so print -1 for them */

            while (s.Count!=0) {

        Console.WriteLine(s.Peek() + " --> " + "-1");

        s.Pop();

        }

    }

    /* Driver program to test above functions */

    public static void Main () {

        int []arr = { 11, 13, 21, 3};

        int n = arr.Length;

        printNSE(arr, n);

    }

}




OUTPUT:

11 -- 3
13 -- 3
21 -- 3
3 -- -1

CREDITS: https://www.geeksforgeeks.org/next-smaller-element/