Example: Find Second Smallest and Largest in Single Pass in C

// Find Second Smallest and Largest in Single Pass
#include <stdio.h>
#include <limits.h> // For INT_MAX and INT_MIN

void findSecondMinMaxSinglePass(int arr[], int n) {
    if (n < 2) {
        printf("Array must have at least two elements.\n");
        return;
    }

    // Initialize with extreme values
    int smallest = INT_MAX, secondSmallest = INT_MAX;
    int largest = INT_MIN, secondLargest = INT_MIN;

    for (int i = 0; i < n; i++) {
        // Logic for smallest and second smallest
        if (arr[i] < smallest) {
            secondSmallest = smallest; // Current smallest becomes second smallest
            smallest = arr[i];         // Current element becomes new smallest
        } else if (arr[i] < secondSmallest && arr[i] != smallest) {
            secondSmallest = arr[i]; // Current element is between smallest and secondSmallest
        }

        // Logic for largest and second largest
        if (arr[i] > largest) {
            secondLargest = largest; // Current largest becomes second largest
            largest = arr[i];        // Current element becomes new largest
        } else if (arr[i] > secondLargest && arr[i] != largest) {
            secondLargest = arr[i]; // Current element is between largest and secondLargest
        }
    }

    if (secondSmallest != INT_MAX) {
        printf("Second smallest element (single-pass approach): %d\n", secondSmallest);
    } else {
        printf("Second smallest element not found (all elements might be same or array too small).\n");
    }

    if (secondLargest != INT_MIN) {
        printf("Second largest element (single-pass approach): %d\n", secondLargest);
    } else {
        printf("Second largest element not found (all elements might be same or array too small).\n");
    }
}

int main() {
    int arr[] = {12, 35, 1, 10, 34, 1};
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Original array: ");
    for (int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    findSecondMinMaxSinglePass(arr, n);

    int arr2[] = {5, 5, 5, 5};
    int n2 = sizeof(arr2) / sizeof(arr2[0]);
    printf("\nOriginal array 2: ");
    for (int i = 0; i < n2; i++) {
        printf("%d ", arr2[i]);
    }
    printf("\n");
    findSecondMinMaxSinglePass(arr2, n2);
    
    int arr4[] = {10, 20, 30};
    int n4 = sizeof(arr4) / sizeof(arr4[0]);
    printf("\nOriginal array 4: ");
    for (int i = 0; i < n4; i++) {
        printf("%d ", arr4[i]);
    }
    printf("\n");
    findSecondMinMaxSinglePass(arr4, n4);

    int arr3[] = {7};
    int n3 = sizeof(arr3) / sizeof(arr3[0]);
    printf("\nOriginal array 3: ");
    for (int i = 0; i < n3; i++) {
        printf("%d ", arr3[i]);
    }
    printf("\n");
    findSecondMinMaxSinglePass(arr3, n3);

    return 0;
}