function log() {

    var i = 0,

        str = '',

        args = [].slice.call(arguments);

    j++;

    if (isRepeat(args)) {

        k++;

        return;

    }

    while(i < args.length) {

        str += chars[args[i]];

        i++;

    }

    console.log(str);

}

function count(obj) {

    var i = 0;

    for (var p in obj) {

        if (obj.hasOwnProperty(p)) {

            i++;

        }

    }

    return i;

}

function isRepeat(arr) {

    var i = 0,

        obj = {};

    while(i < arr.length) {

        obj[typeof arr[i] + arr[i]] = 1;

        if (count(obj) === i) {

            return true;

        }

        i++;

    }

    return false;

}

function loop(min, max, fn, count) {

    var i, args;

    i = min;

    count++;

    args = [].slice.call(arguments, 0);

    while(i < max) {

        var iargs = args.slice(0);

        iargs.push(i);

        fn.apply(window, iargs.slice(4));

        if (count < max - min) {

            arguments.callee.apply(window, iargs);

        }

        i++;

    }

}

var chars = ['a', 'b', 'c', 'd', 'e', 'f'];

var j = 0, k = 0;

loop(0, chars.length, log, 0);

console.log('共执行', j, '次, 不允许单字符重用有', j - k, '次, 允许单字符重用有', k, '次');