vector<int> nextGreaterElement(vector<int>& nums1, vector<int>& nums2) {
        int n1=nums1.size();
        int n2=nums2.size();
        stack<int>st;
        vector<int>ans;
        unordered_map<int,int>umap;
        
        for(int i=n2-1;i>=0;i--){
            while(!st.empty()&&st.top()<nums2[i]){
                st.pop();
        }
        if(st.empty()){
            umap[nums2[i]]=-1;
        }
        else{
            umap[nums2[i]]=st.top();
        }
        st.push(nums2[i]);
        
    }
    for(int i=0;i<n1;i++){
        ans.push_back(umap[nums1[i]]);
    }
    return ans;
    }