求數組值與最近的比當前值大的數的差值 Daily Temperatures

問題：

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].

解決：

① 給出一個數組，對每一個位置，在當前位置後面找出最近的比當前位置大的數，求出位置差。維護一個降序的棧，當出現比棧中一些數大的數的時候，把那些數出棧，並保存好位置差，而後把當前的數壓入棧，這樣就能夠實現要求。

class Solution { //54ms
    public int[] dailyTemperatures(int[] temperatures) {
        Stack<Integer> stack = new Stack<>();
        int[] res = new int[temperatures.length];
        for (int i = 0;i < temperatures.length;i ++){
            while (! stack.isEmpty() && temperatures[i] > temperatures[stack.peek()]){
                int index = stack.pop();
                res[index] = i - index;
            }
            stack.push(i);
        }
        return res;
    }
}