#25 Medium Time O(n) Space O(n) Animated

Daily Temperatures

Given daily temperatures, return number of days to wait for a warmer temperature.

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2 Trace
3 Explain
4 Implement

Pattern LIFO state for unresolved work

Keep only items whose matching decision has not been made yet.

Approach: Monotonic Decreasing Stack

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Core Insight

Keep only items whose matching decision has not been made yet.

Common Pitfall

Check that the stack is non-empty before reading its top.

Description

Given daily temperatures, return number of days to wait for a warmer temperature.

Constraints

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

Solution — Monotonic Decreasing Stack

TimeO(n) SpaceO(n)

Implementation Plan

Translate the invariant into these small, testable moves.

Read one item at a time.
Push unresolved work.
Match or remove work when its partner arrives.
Validate the final stack state.

def dailyTemperatures(temperatures):
    res = [0] * len(temperatures)
    stack = [] # pair: [temp, index]
    
    for i, t in enumerate(temperatures):
        while stack and t > stack[-1][0]:
            stackT, stackInd = stack.pop()
            res[stackInd] = i - stackInd
        stack.append([t, i])
        
    return res

Generate Parentheses

Car Fleet

Daily Temperatures

Steps

Description

Constraints

Tags

Solution — Monotonic Decreasing Stack