3185. Count Pairs That Form a Complete Day II

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.

class Solution {
public:
    long long countCompleteDayPairs(vector<int>& hours) {
        unordered_map<int, long long> freq;
        long long res = 0;
        for(auto& h : hours) {
            int t = h % 24, x = (24 - t + 24) % 24;
            res += freq[x];
            freq[t]++;
        }
        return res;
    }
};