rotateArray.js

// Rotate an array to right by n.
function rotate(a, n) {
    // Convert negative to positive.
    if (n < 0) n = ((n % a.length) + a.length);
    n = n % a.length;
    
    reverse(a, 0, a.length); // Move to bottom to reverse to the left.
    reverse(a, 0, n);
    reverse(a, n, a.length); 
}

// Reverse the subarray.
function reverse(a, start, end) {
    var temp;
    var mid = start + ((end - start)/2 | 0); // Round to int.
    for (var i = start; i < mid; i++) {
        temp = a[i];
        a[i] = a[start + end - i - 1];
        a[start + end - i - 1] = temp;
    }
}