Problem Description
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.
Key Insights
- We need to determine the number of days until a warmer temperature for each day in the input array.
- A naive approach would involve nested loops leading to O(n^2) time complexity, which is inefficient for large input sizes.
- A more efficient solution can be achieved using a monotonic stack to keep track of indices of temperatures in a way that allows us to efficiently find the next warmer temperature.
Space and Time Complexity
Time Complexity: O(n)
Space Complexity: O(n)
Solution
We can solve this problem using a stack data structure. The approach involves iterating through the temperatures array while maintaining a stack that stores indices of the temperatures in a decreasing order. For each temperature, we check if it is warmer than the temperature represented by the index at the top of the stack. If so, we pop from the stack, calculate the number of days to wait, and continue this until the stack is either empty or the current temperature is not warmer. This ensures that we efficiently determine the number of days for each temperature in a single pass.