Problem 24

twenty-four.js

var permutations = [],
    numberArray = '1234567890'.split('');

function swap(a, b) {
    var tmp = numberArray[a];
    numberArray[a] = numberArray[b];
    numberArray[b] = tmp;
}

// Use Heap's algorithm to swap around numbers
// @see https://en.wikipedia.org/wiki/Heap's_algorithm
function getPermutations(n) {
    if (n == 1) {
        permutations.push(numberArray.join(''));
    } else {
        for (var i = 0; i != n; ++i) {
            getPermutations(n - 1);
            swap(n % 2 ? 0 : i, n - 1);
        }
    }
}
getPermutations(numberArray.length);
permutations.sort();
document.body.innerHTML = permutations[1000000-1];