Next_Greater_Element-1.cpp

Problem :- The next greater element of some element x in an array is the first greater element that is to the right of x in the same array.

You are given two distinct 0-indexed integer arrays nums1 and nums2, where nums1 is a subset of nums2.

For each 0 <= i < nums1.length, find the index j such that nums1[i] == nums2[j] and determine the next greater element of nums2[j] in nums2. If there is no next greater element, then the answer for this query is -1.

Return an array ans of length nums1.length such that ans[i] is the next greater element as described above.

 

Example 1:

Input: nums1 = [4,1,2], nums2 = [1,3,4,2]
Output: [-1,3,-1]
Explanation: The next greater element for each value of nums1 is as follows:
- 4 is underlined in nums2 = [1,3,4,2]. There is no next greater element, so the answer is -1.
- 1 is underlined in nums2 = [1,3,4,2]. The next greater element is 3.
- 2 is underlined in nums2 = [1,3,4,2]. There is no next greater element, so the answer is -1.
  
  
  Solution:-
     class Solution {
public:
    vector<int> nextGreaterElement(vector<int>& n1, vector<int>& n2) {
    int x;
    vector<int> ans;
    stack<int> p;
    for(int i=0;i<n1.size();i++)
    {
    int ref=n1[i];
    int t=find(n2.begin(),n2.end(),ref)-n2.begin();
    if(t==n2.size())
    {
        ans.push_back(-1);
    }
    else{
        bool f=false;
        while(t<n2.size()-1)
        {
            p.push(n2[++t]);
            if(p.top()>ref)
            {
                ans.push_back(p.top());
                f=true;
                break;
            }
        }
        while(!p.empty())p.pop();
        if(f==true)continue;
        else ans.push_back(-1);
    }
    }
        return ans;
    }
};