6     2      6
      6     -1



s//6,2
min=6
==========================================================
https://www.naukri.com/code360/problems/least-greater-element_1164266?leftPanelTabValue=SUBMISSION


import java.util.* ;
import java.io.*; 
public class Solution {
    public static int[] leastGreaterElement(int[] arr) {
        // Write your code here
        ArrayList<Integer> al=new ArrayList<>();
        Stack<Integer> s=new Stack<>();
        int min=Integer.MAX_VALUE;
        boolean found=false;
        for(int i=arr.length-1;i>=0;i--){
            found=false;
            min=Integer.MAX_VALUE;
            int x=arr[i];
           
            for(Integer k:s){
                if(x<k){
                   if(k<min){
                       found=true;
                       min=k;
                   }
                }
            }

            if(s.isEmpty()){
                al.add(-1);
            }else{
                if(found==false){
                    al.add(-1);
                }else{
                 al.add(min);
                }
            }
            s.push(x);
        }
        Collections.reverse(al);
        int arr1[]=new int[al.size()];
        int j=0;
        for(Integer i:al){
            arr1[j]=i;
            j++;
        }
        return arr1;
    }
}
========================================================================
https://leetcode.com/problems/asteroid-collision/
=======================================================================
class Solution {
    public int[] asteroidCollision(int[] asteroids) {
        Stack<Integer> stack=new Stack<>();   
        boolean found=false;
        for(int i=0;i<asteroids.length;i++){
            int x=asteroids[i];
            found=false;
            while(!stack.isEmpty() && x<0 && stack.peek()>0){
                if(stack.peek()>Math.abs(x)){
                    break;
                }else if(stack.peek()<Math.abs(x)){
                    stack.pop();
                }else{
                    stack.pop();
                    found=true;
                    break;
                }
            }
            if(found==false){
                if(stack.isEmpty() || x>0 || stack.peek()<0){
                    stack.push(x);
                }
            }
        }
        int c=0;
        int ans[]=new int[stack.size()];
        for(Integer i:stack){
            ans[c]=i;
            c++;
        }
        return ans;
    }
}
=================================================================
[5,10,-20]


first process each and every number 
previous numbers are there in the stack

//5, 10 , 
//5 ,-20

-90  23 

=============================================================
https://leetcode.com/problems/sum-of-subarray-minimums/