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 - 1; i >= 0; i--) {
            if (stack.isEmpty()) {
                result[i] = 0;
                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] = 0;
                } 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;
    }
}