Example: FindSecondSmallest_SinglePass in Java

// FindSecondSmallest_SinglePass
public class Main {
    public static int findSecondSmallestSinglePass(int[] arr) {
        if (arr == null || arr.length < 2) {
            System.out.println("Array must contain at least two elements.");
            return -1;
        }

        // Step 1: Initialize smallest and secondSmallest
        // We can't use arr[0] and arr[1] directly due to potential duplicates or order.
        // Initialize with MAX_VALUE to ensure any array element will be smaller.
        int smallest = Integer.MAX_VALUE;
        int secondSmallest = Integer.MAX_VALUE;

        // Step 2: Iterate through the array once
        for (int num : arr) {
            if (num < smallest) {
                // If current number is smaller than smallest,
                // the old smallest becomes the new secondSmallest,
                // and the current number becomes the new smallest.
                secondSmallest = smallest;
                smallest = num;
            } else if (num < secondSmallest && num != smallest) {
                // If current number is smaller than secondSmallest
                // but not equal to smallest, then it's the new secondSmallest.
                secondSmallest = num;
            }
        }

        // Step 3: Check if a distinct second smallest was found
        if (secondSmallest == Integer.MAX_VALUE) {
            System.out.println("No distinct second smallest element found.");
            return -1;
        }

        return secondSmallest;
    }

    public static void main(String[] args) {
        int[] arr1 = {12, 5, 2, 10, 8, 2, 1};
        System.out.println("Original array: " + java.util.Arrays.toString(arr1));
        System.out.println("Second smallest element (Single Pass): " + findSecondSmallestSinglePass(arr1)); // Output: 5

        int[] arr2 = {7, 7, 3, 3, 5};
        System.out.println("Original array: " + java.util.Arrays.toString(arr2));
        System.out.println("Second smallest element (Single Pass): " + findSecondSmallestSinglePass(arr2)); // Output: 5

        int[] arr3 = {10, 10, 10, 10};
        System.out.println("Original array: " + java.util.Arrays.toString(arr3));
        System.out.println("Second smallest element (Single Pass): " + findSecondSmallestSinglePass(arr3)); // Output: -1

        int[] arr4 = {5};
        System.out.println("Original array: " + java.util.Arrays.toString(arr4));
        System.out.println("Second smallest element (Single Pass): " + findSecondSmallestSinglePass(arr4)); // Output: -1
    }
}