739. Daily Temperatures

Given a list of daily temperatures T, return a list such that, for each day in the input, tells you how many days you would have to wait until a warmer temperature. If there is no future day for which this is possible, put 0 instead.

For example, given the list of temperatures T = [73, 74, 75, 71, 69, 72, 76, 73], your output should be [1, 1, 4, 2, 1, 1, 0, 0].

Note: The length of temperatures will be in the range [1, 30000]. Each temperature will be an integer in the range [30, 100].

class Solution {
public:
    vector<int> dailyTemperatures(vector<int>& T) {
        vector<int> st;
        vector<int> res(T.size(), 0);
        for(int i = T.size() - 1; i >= 0; i--) {
            while(!st.empty() and T[st.back()] <= T[i]) st.pop_back();
            if(!st.empty()) {
                res[i] = st.back() - i;
            }
            st.push_back(i);
        }
        return res;
    }
};

class Solution {
public:
    vector<int> dailyTemperatures(vector<int>& T) {
        int n = T.size();
        vector<int> res(n, 0);
        map<int, int> m;
        for(int i = n - 1; i >= 0; i--) {
            auto it = m.upper_bound(T[i]);
            if(it != end(m)) res[i] = it->second - i;
            m[T[i]] = i;
            it = m.find(T[i]);
            do if(it != begin(m)){
                it = prev(it);
                it->second = i;
            }while(it != begin(m));
        }
        return res;
    }
};