C++ (Coding): First Missing Positive Integer Test

The solution approach of the problem starts by creating an unordered set seen to store the unique positive integers encountered in the input vector nums. This set will help us efficiently check if a number is present in nums. It then iterates through each element i in nums using a range-based for loop. For each positive integer i greater than 0, it inserts i into the seen set. After processing all the elements in nums, the function initializes two variables: i with an initial value of 1 (representing the smallest positive integer) and n as the size of nums. It enters a while loop that continues until i is greater than n. The purpose of this loop is to find the first missing positive integer in the range from 1 to n. Inside the loop, it checks if the current value of i is present in the seen set using the count function. If i is not found in the set, it means i is the first missing positive integer, so it returns i as the result. If i is found in the seen set, it increments i by 1 and continues to the next iteration of the loop to check the next integer. If the while loop completes without finding a missing positive integer, it means all positive integers from 1 to n are present in nums. In this case, the first missing positive integer would be n + 1, so it returns i (which is n + 1) as the result.