JavaScript issue with swapping array elements using destructuring

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1

I’m new to JavaScript and I’m encountering an issue with a coding challenge that involves exchanging two items in an array. Below is my existing code in JavaScript:

/**
 * @param {number[]} values
 * @return {number[][]}
 */
var generatePermutations = function(values) {
    const len = values.length;
    const result = [];
    const swapAndExplore = (index, current) => {
        if (index >= len - 1) {
            result.push([...current]);
            return;
        }

        for (let j = index; j < len; j++) {
            [current[j], current[index]] = [current[index], current[j]];
            swapAndExplore(index + 1, current);
            [current[j], current[index]] = [current[index], current[j]];  
        }
    };
    swapAndExplore(0, [...values]);
    return result;
};
// Example usage
console.log(generatePermutations([1,2,3]));

However, I encountered a runtime error below:

Line 17 in solution.js
            [current[j], current[index]] = [current[index], current[j]];
                                 ^
TypeError: Cannot set properties of undefined (setting '2')

I used the debugger to analyze the code, and it appeared to be error-free before the runtime issue occurred. Even executing this in the developer console of Chrome resulted in the same error message.

In an attempt to resolve the problem, I added a semicolon after the swap line:

        for (let j = index; j < len; j++) {
            [current[j], current[index]] = [current[index], current[j]];
            swapAndExplore(index + 1, current);
            [current[j], current[index]] = [current[index], current[j]];
        }

This has left me puzzled, and unfortunately, I couldn’t find a satisfactory explanation from ChatGPT. I would greatly appreciate any help or insights you could share. Thank you!

2

The error you encountered, TypeError: Cannot set properties of undefined (setting '2'), often indicates that the destructuring assignment is attempting to access a variable that is not properly initialized or does not exist within the array's bounds. In your code, this could be due to inadvertently altering the original array references or indices during the recursion.

The core of the problem lies in overwriting the array elements. When operating in a recursive function like swapAndExplore, making mutable changes such as swapping can lead to unintended behavior if not handled properly. Let's address this by ensuring array integrity through a cloned array.

Here's a refined version of your code:

/**
 * @param {number[]} values
 * @return {number[][]}
 */
var generatePermutations = function(values) {
    const len = values.length;
    const result = [];
    const swapAndExplore = (index, current) => {
        if (index >= len) {
            result.push([...current]);
            return;
        }

        for (let j = index; j < len; j++) {
            // Clone current array to ensure permutations are made on a new array
            let newCurrent = [...current];
            [newCurrent[j], newCurrent[index]] = [newCurrent[index], newCurrent[j]];
            swapAndExplore(index + 1, newCurrent);
        }
    };
    swapAndExplore(0, [...values]);
    return result;
};
// Example usage
console.log(generatePermutations([1,2,3]));

This updated version introduces several key adjustments:

  • Array Cloning: Within the loop, we create newCurrent, which is a copied version of the input array. This ensures that each permutation operates independently, preventing alterations from being carried forward within the recursive stack.

Since the permutations are conducted on cloned versions of the array, the original integrity of the array remains unchanged. This prevents the undefined index error you're experiencing. I hope this helps resolve the issue and clarifies how to handle array permutations more effectively in JavaScript.