LeetCode-in-Java

3184. Count Pairs That Form a Complete Day I

Easy

Given an integer array hours representing times in hours, return an integer denoting the number of pairs i, j where i < j and hours[i] + hours[j] forms a complete day.

A complete day is defined as a time duration that is an exact multiple of 24 hours.

For example, 1 day is 24 hours, 2 days is 48 hours, 3 days is 72 hours, and so on.

Example 1:

Input: hours = [12,12,30,24,24]

Output: 2

Explanation:

The pairs of indices that form a complete day are (0, 1) and (3, 4).

Example 2:

Input: hours = [72,48,24,3]

Output: 3

Explanation:

The pairs of indices that form a complete day are (0, 1), (0, 2), and (1, 2).

Constraints:

• 1 <= hours.length <= 100
• 1 <= hours[i] <= 109

Solution

public class Solution {
    public int countCompleteDayPairs(int[] hours) {
        int[] modular = new int[26];
        int ans = 0;
        for (int hour : hours) {
            int mod = hour % 24;
            ans += modular[24 - mod];
            if (mod == 0) {
                modular[24]++;
            } else {
                modular[mod]++;
            }
        }
        return ans;
    }
}

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