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].

分析：

为了找到后面过了几天会有比当前值更大的值，所以，我们需要从尾遍历，我们用一个stack来存当前最大值。

 public class Solution {
     public int[] dailyTemperatures(int[] T) {
         if (T == null) return null;
         int[] result = new int[T.length];
         Stack<Temperature> stack = new Stack<>();

         for (int i = T.length - ; i >= ; i--) {
             if (stack.isEmpty()) {
                 result[i] = ;
                 stack.push(new Temperature(T[i], i));
             } else if (stack.peek().value > T[i]) {
                 result[i] = stack.peek().index - i;
                 stack.push(new Temperature(T[i], i));
             } else {
                 while (!stack.isEmpty() && stack.peek().value <= T[i]) {
                     stack.pop();
                 }
                 if (stack.isEmpty()) {
                     result[i] = ;
                 } else {
                     result[i] = stack.peek().index - i;
                 }
                 stack.push(new Temperature(T[i], i));
             }
         }
         return result;
     }
 }

 class Temperature {
     int value;
     int index;

     public Temperature(int value, int index) {
         this.value = value;
         this.index = index;
     }
 }