leetcode--496

   vector<int> nextGreaterElement(vector<int>& findNums, vector<int>& nums) {
        vector<int>v;
        stack <int> s;
        map<int,int> m;
        for(int i=nums.size()-1;i>=0;i--)
        {
            while(!s.empty()&&s.top()<=nums[i])
            s.pop();
            m[nums[i]]=s.empty()?-1:s.top();
            s.push(nums[i]);
        }
        for(int i=0;i<findNums.size();i++)
        {
            v.push_back(m[findNums[i]]);
        }
        return v;
    }