求数组值与最近的比当前值大的数的差值 Daily Temperatures

问题：

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].

解决：

① 给出一个数组，对每一个位置，在当前位置后面找出最近的比当前位置大的数，求出位置差。维护一个降序的栈，当出现比栈中一些数大的数的时候，把那些数出栈，并保存好位置差，而后把当前的数压入栈，这样就能够实现要求。

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;
    }
}