Count Pairs That Form a Complete Day II - Solution & Explanation

This is a straightforward approach where you iterate over all possible pairs in the array and check if their sum is a multiple of 24. Although not optimal, it's the simplest solution to understand the problem and attempt manual calculations for small inputs.

In this C code, we define a function countCompleteDays which processes all possible pairs using nested loops, checking if their sum is divisible by 24 (i.e., (hours[i] + hours[j]) % 24 == 0). The time complexity is O(n^2) since we are checking each pair, and the space complexity is O(1) because we are not using additional storage proportional to the input size.

This approach optimizes the search for pairs whose sums are multiples of 24 by using a hash map (or dictionary) to track previously seen remainders when each hour is divided by 24. This reduces time complexity to linear.

This C code uses an array remainderCount of size 24 to keep track of the frequency of remainders when elements of hours are divided by 24. It efficiently counts pairs forming complete days by using these remainders.