0739.Daily Temperatures

Link: 739. Daily Temperatures
Track: Tiktok Tag

Question

Restate the problem

• Given an integer array temperatures, where temperatures[i] is the temperature on day i
• For each day i, find the number of days until a warmer temperature occurs.
  • If there is no future day with a warmer temperature, answer[i] = 0.
• Return answer

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Method 1 - stack

Method 1 - Monotonic Stack

Approach

• Stack to stores indices idx
• Temperatures on those indices are strictly decreasing
• While temp > stack[-1] the day at stack top, we can resolve that previous day:
  • pre_idx = stack.pop()
  • ans[pre_idx] = idx - pre_idx

Complexity

• Time Complexity: O(n)
• Space Complexity: O(n)

Edge Case

• temperatures = [] → return []
• Strictly decreasing: [80, 79, 78] → [0, 0, 0] (no one gets popped)

Code

class Solution:
    def dailyTemperatures(self, temperatures: List[int]) -> List[int]:
        stack = []
        ans = [0] * len(temperatures)
 
        for idx, temp in enumerate(temperatures):
            
            while stack and temperatures[stack[-1]] < temp:
                pre_idx = stack.pop()
                ans[pre_idx] = idx - pre_idx
            
            stack.append(idx)
        
        return ans

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History

• Feb-11-2026 Peeked