Example: Find Symmetric Pairs (Optimized with Printed Flags) in C

// Find Symmetric Pairs (Optimized with Printed Flags)
#include <stdio.h>
#include <stdbool.h> // Required for boolean type

// Structure to represent a pair of integers
struct Pair {
    int first;
    int second;
};

int main() {
    // Step 1: Define the array of pairs
    struct Pair pairs[] = {{1, 2}, {3, 4}, {5, 2}, {2, 1}, {4, 3}, {6, 7}, {7, 6}};
    int n = sizeof(pairs) / sizeof(pairs[0]);

    // Step 2: Create a boolean array to track if a pair has been printed
    bool was_printed[n];
    for (int i = 0; i < n; i++) {
        was_printed[i] = false; // Initialize all flags to false
    }

    printf("Original Pairs:\n");
    for (int i = 0; i < n; i++) {
        printf("(%d, %d) ", pairs[i].first, pairs[i].second);
    }
    printf("\n\n");

    printf("Symmetric Pairs:\n");
    // Step 3: Iterate through each pair using the outer loop
    for (int i = 0; i < n; i++) {
        // Step 4: Check if the current pair has already been marked as part of a symmetric pair
        if (!was_printed[i]) {
            // Step 5: Look for its symmetric counterpart in the subsequent pairs
            for (int j = i + 1; j < n; j++) {
                // Step 6: If pairs[j] is the symmetric counterpart AND it hasn't been printed yet
                if (!was_printed[j] &&
                    pairs[i].first == pairs[j].second &&
                    pairs[i].second == pairs[j].first) {

                    printf("(%d, %d) and (%d, %d)\n", pairs[i].first, pairs[i].second, pairs[j].first, pairs[j].second);
                    was_printed[i] = true; // Mark both pairs as printed
                    was_printed[j] = true;
                    break; // Move to the next unique pair in the outer loop after finding a match
                }
            }
        }
    }

    return 0;
}