NGE.java

//leetcode --> 496. Next Greater Element I
import java.util.*;
class Hactober {
    public static int[] nextGreaterElement(int[] nums1, int[] nums2) {
        HashMap<Integer,Integer> map = new HashMap<>();
        Stack<Integer> s = new Stack<>();
        for(int i:nums2){
            while(!s.isEmpty()&&s.peek()<i)map.put(s.pop(),i);
            s.push(i);
        }
        for(int i=0;i<nums1.length;i++){
            nums1[i]=map.getOrDefault(nums1[i],-1);
        }
        return nums1;
    }
   public static void main(String[] args){
        int[] arr1 = {4,1,2};
        int[] arr2 = {1,3,4,2};
        int[] res = nextGreaterElement(arr1,arr2);
        for(int i : res)System.out.print(i + " ");
   }
}