下一个更大的元素

    vector<int> nextGreaterElement(vector<int>& nums1, vector<int>& nums2) {
        if(nums1.empty() || nums2.empty())return {};
        int len = nums2.size();
        unordered_map<int, int> m;
        stack<int> s;
        for(int i = len - 1;i >= 0;--i){
            while(!s.empty() && nums2[i] >= s.top())s.pop();
            if(s.empty())m[nums2[i]] = -1;
            else m[nums2[i]] = s.top();
            s.push(nums2[i]);
        }
        int n = nums1.size();
        vector<int> ans(n, 0);
        for(int i = 0;i < n;++i){
            ans[i] = m[nums1[i]];
        }
        return ans;
    }