Example: Find Second Smallest in Single Pass in C

// Find Second Smallest in Single Pass
#include <stdio.h>
#include <limits.h> // Required for INT_MAX

int main() {
    int arr[] = {5, 2, 8, 1, 9, 2}; // Example array
    int n = sizeof(arr) / sizeof(arr[0]);

    // Step 1: Handle edge cases for array size
    if (n < 2) {
        printf("Array size must be at least 2 to find the second smallest element.\n");
        return 1;
    }

    // Step 2: Initialize first_smallest and second_smallest
    // Initialize with INT_MAX to ensure any array element will be smaller
    int first_smallest = INT_MAX;
    int second_smallest = INT_MAX;

    // Step 3: Iterate through the array
    for (int i = 0; i < n; i++) {
        // If current element is smaller than first_smallest
        if (arr[i] < first_smallest) {
            second_smallest = first_smallest; // The old first_smallest becomes the new second_smallest
            first_smallest = arr[i];          // Current element is the new first_smallest
        }
        // If current element is between first_smallest and second_smallest
        else if (arr[i] < second_smallest && arr[i] != first_smallest) {
            second_smallest = arr[i]; // Current element is the new second_smallest
        }
    }

    // Step 4: Check if a valid second smallest element was found
    if (second_smallest == INT_MAX) {
        printf("No second smallest element found (all elements might be the same).\n");
    } else {
        printf("The second smallest element is: %d\n", second_smallest);
    }

    return 0;
}