Example: Hash Map Duplicate Finder in C++

// Hash Map Duplicate Finder
    #include <iostream>
    #include <vector>
    #include <unordered_set> // For std::unordered_set

    int findDuplicateHashMap(const std::vector<int>& nums) {
        // Step 1: Create an unordered set to store unique numbers encountered
        std::unordered_set<int> seen_numbers;

        // Step 2: Iterate through the input numbers
        for (int num : nums) {
            // Step 3: Check if the number is already in the set
            if (seen_numbers.count(num)) {
                // Step 4: If yes, it's a duplicate
                return num;
            }
            // Step 5: If not, add it to the set
            seen_numbers.insert(num);
        }
        // Step 6: Should not be reached under problem constraints
        return -1;
    }

    int main() {
        std::vector<int> nums = {1, 3, 4, 2, 2};
        int duplicate = findDuplicateHashMap(nums);

        if (duplicate != -1) {
            std::cout << "The duplicate number is: " << duplicate << std::endl;
        } else {
            std::cout << "No duplicate found." << std::endl;
        }

        std::vector<int> nums2 = {3, 1, 3, 4, 2};
        duplicate = findDuplicateHashMap(nums2);
        if (duplicate != -1) {
            std::cout << "The duplicate number is: " << duplicate << std::endl;
        } else {
            std::cout << "No duplicate found." << std::endl;
        }

        return 0;
    }