You are given an integer array digits, where each element is a digit. The array may contain duplicates. You need to find all the unique integers that follow the given requirements: The integer consists of the concatenation of three elements from di

findEvenNumbers.js

/**
 * Finds all three-digit even numbers that can be formed using the given digits.
 * @param {number[]} digits - An array of digits (0-9).
 * @return {number[]} - An array of unique three-digit even numbers.
 */
var findEvenNumbers = function(digits) {
    const arr = []; // Stores valid even numbers
    const ct = Array(10).fill(0); // Count occurrences of each digit (0-9)

    // Count frequency of digits in the input array
    digits.forEach(x => {
        ct[x] += 1;
    });

    // Possible values for each digit position
    const pos1 = [1,2,3,4,5,6,7,8,9]; // First digit cannot be 0
    const pos2 = [0,1,2,3,4,5,6,7,8,9]; // Second digit can be any value
    const pos3 = [0,2,4,6,8]; // Last digit must be even
    const num = [-1, -1, -1]; // Temporary storage for current number

    // Iterate over possible first digits
    for(let i = 0; i < pos1.length; i++) {
        if (ct[pos1[i]] === 0) continue; // Skip if digit is unavailable

        num[0] = pos1[i];
        ct[pos1[i]] -= 1; // Use this digit
        
        // Iterate over possible second digits
        for(let j = 0; j < pos2.length; j++) {
            if (ct[pos2[j]] === 0) continue; // Skip if digit is unavailable
            
            num[1] = pos2[j];
            ct[pos2[j]] -= 1; // Use this digit

            // Iterate over possible third digits (even numbers)
            for(let k = 0; k < pos3.length; k++) {
                if (ct[pos3[k]] === 0) continue; // Skip if digit is unavailable
                
                // Construct and store the number
                arr.push(Number(`${num[0]}${num[1]}${pos3[k]}`));
            }

            ct[pos2[j]] += 1; // Restore count for backtracking
        }

        ct[pos1[i]] += 1; // Restore count for backtracking
    }

    return arr;
};