739. Daily Temperatures

class Solution {
public:
    vector<int> dailyTemperatures(vector<int>& temperatures) {
        stack<int> st;
        vector<int> res(temperatures.size());
        for (int i = temperatures.size() -1; i >= 0; i--) {
            while (!st.empty() && temperatures[i] >= temperatures[st.top()])
                st.pop();
            if (st.empty())
                res[i] = 0;
            else
                res[i] = st.top() - i;
            st.push(i);
        }
        return res;
    }
};