function generateDeck(n) {
    var arr = [];
    for (var i = 1; i <= n; i ++) {
        arr.push(i);
    }
    return arr;
}

function shuffle(c, deck) {
    var arr = [];
    var n = deck.length;
    var left = c;
    var right = n - c;

    if (left <= right) {
        for ( var i= 0; i < c; i++) {
            arr.splice(0, 0, deck[c-i-1]);
            arr.splice(0, 0, deck[n-1-i]);
        }
    }
    if (left < right && left != right) {
        for (var i=n-c-1; i > c -1; i--) {
            arr.splice(0, 0, deck[i]);
        }
    }
    if (left > right) {
        for (var i = 0; i < c; i++) {
            if (i < right) {
                arr.splice(0,0, deck[c-i-1]);
                arr.splice(0,0, deck[n-1-i]);
            }
        }
        for (var i = n -(2*right) -1; i >=0; i--) {
            arr.splice(i,0, deck[i]);
        }
    }
    return arr;
}

function getIterations(arr, c) {
    var map = new Map();
    var shuffled = shuffle(c, arr);

    for (var i = 0; i < arr.length; i ++) {
        for (var j = 0; j < shuffled.length; j++) {
            if (arr[i] === shuffled[j]) {
                map.set(i, j);
            }
        }
    }
    return map;
}

function getIndexIterations(i, arr, c, map) {
    var end = i;
    var current = map.get(i);
    var count = 1;
    while (current != end) {
        current = map.get(current);
        count += 1;
    }
    return count;
}

function checkCountForAllIndices(arr, c) {
    var counts = [];
    var map = getIterations(arr, c);
    for (var i = 0; i < arr.length; i++) {
        var temp = getIndexIterations(i, arr, c, map);
        counts.push(temp)
    }
    return lcmm(counts)
}

function gcd(a, b) {
    var t;
    while (b != 0){
        t = b;
        b = a % b;
        a = t;
    }
    return a;
}

function lcm(a, b) {
    return (a * b / gcd(a, b));
}

function lcmm(args) {
    if(args.length == 2) {
        return lcm(args[0], args[1]);
    } else {
        var arg0 = args[0];
        args.shift();
        return lcm(arg0, lcmm(args));
    }
}
console.time('start');
console.log(checkCountForAllIndices(generateDeck(1002), 101));
console.timeEnd('start')
// prints out:
// 5812104600
// start: 122.344ms