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3418. Count Pairs That Form a Complete Day II

My accepted Python solution to LeetCode problem 3418, Count Pairs That Form a Complete Day II, running in 1073ms.

  • Difficulty: Medium
  • Python
  • Runtime 1073ms
  • Memory 69.2MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

Python

Accepted on LeetCode — runtime 1073ms, memory 69.2MB, accepted 2025-12-30.

python
class Solution:
    def countCompleteDayPairs(self, hours: List[int]) -> int:
        from collections import defaultdict
        
        # Use hash map to count remainders
        remainder_count = defaultdict(int)
        count = 0
        
        for h in hours:
            rem = h % 24
            # Need a pair with remainder such that (rem + other) % 24 == 0
            # Other should be (24 - rem) % 24
            target = (24 - rem) % 24
            count += remainder_count[target]
            remainder_count[rem] += 1
        
        return count

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