Daily Temperatures

Problem

Given an array of integers temperatures representing 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.

Examples

The brute-force approach

For each day, scan forward until you find a day with a higher temperature. Record the distance.

answer = [0] * len(temperatures)

for i in range(len(temperatures)):
    for j in range(i + 1, len(temperatures)):   # scan forward
        if temperatures[j] > temperatures[i]:
            answer[i] = j - i
            break

return answer

For each of the n days, you might scan up to n more days, making it O(n²). A monotonic stack lets you process each day exactly once: when you find a warmer day, resolve all the colder days waiting in the stack.

Spotting the pattern

This is a Stack problem. The key question to ask yourself:

For each day, how do I find the next warmer one without comparing it to every future day?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.