739. Daily Temperatures

Link: https://leetcode.cn/problems/daily-temperatures/

Question

difficulty: mid
adj diff: 2

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead.

Example 1:

Input: temperatures = [73,74,75,71,69,72,76,73]
Output: [1,1,4,2,1,1,0,0]

Example 2:

Input: temperatures = [30,40,50,60]
Output: [1,1,1,0]

Example 3:

Input: temperatures = [30,60,90]
Output: [1,1,0]
Constraints:

    1 <= temperatures.length <= 105
    30 <= temperatures[i] <= 100

Code

public int[] dailyTemperatures(int[] temperatures) {
    int len = temperatures.length;
    int[] ans = new int[len];
    Stack<Integer> stack = new Stack<Integer>();

    for (int i = len - 1; i >= 0; i--) {
        while (!stack.isEmpty() && temperatures[stack.peek()] <= temperatures[i]) {
            stack.pop();
        }
        ans[i] = stack.isEmpty() ? 0 : stack.peek() - i;
        stack.push(i);
    }
    return ans;
}