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