原题链接在这里：https://leetcode.com/problems/daily-temperatures/
题目：
Given a list of daily temperatures, produce a list 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 temperatures = [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].
题解：
Stack<Integer> stk里存index, 若当前temperature 更高, 就一直pop出来index, 计算天数差值保存.
最后stk中剩余的index说明这些位置上没有更加暖和的天气, 存0.
Time Complexity: O(n). n = T.length.
Space: O(n).
AC Java:
class Solution {
public int[] dailyTemperatures(int[] T) {
if(T == null || T.length == 0){
return T;
}
int len = T.length;
int [] res = new int[len];
Stack<Integer> stk = new Stack<Integer>();
for(int i = len-1; i>=0; i--){
while(!stk.isEmpty() && T[i]>=T[stk.peek()]){
stk.pop();
}
res[i] = stk.isEmpty() ? 0 : stk.peek()-i;
stk.push(i);
}
return res;
}
}