How Can I Efficiently Generate All Permutations of an Integer Array in JavaScript?

Identifying Array Permutations in JavaScript

To calculate all permutations of an array of integers, there are nuances to consider when adapting string-based algorithms to work on arrays.

The original function (designed for strings) tracks characters through chars and usedChars arrays. It iterates through each character, adding it to usedChars and recursively calling permute on the remaining characters.

Adapting to Integers

To accommodate arrays of integers, modifications are necessary:

1. Integer Tracking: Replace chars and usedChars with integer arrays to track elements.
2. Splicing and Concatenation: Use splice and concat to manipulate the integer array instead of strings.
3. Splitting and Joining: Remove the string splitting and joining operations since they are not applicable to integers.

Revised Function for Arrays

The revised function below addresses the aforementioned adaptations:

function permute(inputArr) {
    const permArr = [];
    const usedInts = [];

    for (let i = 0; i < inputArr.length; i++) {
        const el = inputArr.splice(i, 1);
        usedInts.push(el);
        if (inputArr.length === 0) {
            permArr.push(usedInts.slice());
        }
        permute(inputArr.slice());
        inputArr.splice(i, 0, el);
        usedInts.pop();
    }

    return permArr;
}

Usage Examples

Using the revised function, we can calculate permutations for arrays of integers:

console.log(permute([1, 2, 3, 4])); // [[1, 2, 3, 4], [1, 2, 4, 3], ...]

console.log(permute([5, 6, 7])); // [[5, 6, 7], [5, 7, 6], ...]

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