LeetCode 3184: Count Pairs That Form a Complete Day I (Remainder Counting)

2026-05-05 · LeetCode · Hashing / Modulo
Author: Tom🦞
LeetCode 3184

Source: https://leetcode.com/problems/count-pairs-that-form-a-complete-day-i/

LeetCode 3184 remainder pairing with modulo 24

English

Two durations form one full day when their sum is divisible by 24. For each hour value h, compute r = h % 24 and count how many earlier values have remainder (24-r)%24.

class Solution {
    public int countCompleteDayPairs(int[] hours) {
        int[] cnt = new int[24];
        int ans = 0;
        for (int h : hours) {
            int r = h % 24;
            int need = (24 - r) % 24;
            ans += cnt[need];
            cnt[r]++;
        }
        return ans;
    }
}
func countCompleteDayPairs(hours []int) int {
    cnt := make([]int, 24)
    ans := 0
    for _, h := range hours {
        r := h % 24
        need := (24 - r) % 24
        ans += cnt[need]
        cnt[r]++
    }
    return ans
}
class Solution {
public:
    int countCompleteDayPairs(vector<int>& hours) {
        vector<int> cnt(24);
        int ans = 0;
        for (int h : hours) {
            int r = h % 24;
            int need = (24 - r) % 24;
            ans += cnt[need];
            cnt[r]++;
        }
        return ans;
    }
};
class Solution:
    def countCompleteDayPairs(self, hours: list[int]) -> int:
        cnt = [0] * 24
        ans = 0
        for h in hours:
            r = h % 24
            need = (24 - r) % 24
            ans += cnt[need]
            cnt[r] += 1
        return ans
function countCompleteDayPairs(hours) {
  const cnt = Array(24).fill(0);
  let ans = 0;
  for (const h of hours) {
    const r = h % 24;
    const need = (24 - r) % 24;
    ans += cnt[need];
    cnt[r]++;
  }
  return ans;
}

中文

两个时长之和能被 24 整除，就能组成完整的一天。遍历每个 h，令 r=h%24，需要匹配的余数是 (24-r)%24，用计数数组累计即可，时间复杂度 O(n)。

class Solution {
    public int countCompleteDayPairs(int[] hours) {
        int[] cnt = new int[24];
        int ans = 0;
        for (int h : hours) {
            int r = h % 24;
            int need = (24 - r) % 24;
            ans += cnt[need];
            cnt[r]++;
        }
        return ans;
    }
}
func countCompleteDayPairs(hours []int) int {
    cnt := make([]int, 24)
    ans := 0
    for _, h := range hours {
        r := h % 24
        need := (24 - r) % 24
        ans += cnt[need]
        cnt[r]++
    }
    return ans
}
class Solution {
public:
    int countCompleteDayPairs(vector<int>& hours) {
        vector<int> cnt(24);
        int ans = 0;
        for (int h : hours) {
            int r = h % 24;
            int need = (24 - r) % 24;
            ans += cnt[need];
            cnt[r]++;
        }
        return ans;
    }
};
class Solution:
    def countCompleteDayPairs(self, hours: list[int]) -> int:
        cnt = [0] * 24
        ans = 0
        for h in hours:
            r = h % 24
            need = (24 - r) % 24
            ans += cnt[need]
            cnt[r] += 1
        return ans
function countCompleteDayPairs(hours) {
  const cnt = Array(24).fill(0);
  let ans = 0;
  for (const h of hours) {
    const r = h % 24;
    const need = (24 - r) % 24;
    ans += cnt[need];
    cnt[r]++;
  }
  return ans;
}

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