alert(isTwinShuffle("ABACBDECDE"));

​

function isTwinShuffle(str) {

    var formsShuffle = function(a, str) {

        var len = str.length,

            b = a;

        for (var i = 0; i < a.length; i++) {

            for (var j = j || 0; j < str.length; j++) {

                if (a[i] === str[j]) {

                    str = str.split("");

                    str.splice(j, 1);

                    str = str.join("");

                    break;

                }

            }

        }

        if (str.length !== (len - a.length)) return false;

        if (b !== str) return false;

        return true;

    };

    var permutations = function(str, head) {

        if (str.length <= 1) return [head + str];

        head = head || "";

        var list = [];

        for (var i = 0; i < str.length; i++) {

            list = list.concat(permutations(str.slice(0, i) + str.slice(i + 1), head + str[i]));

        }

        return list;

    };

​

    var letters = {};

    for (var i = 0; i < str.length; i++) {

        var chr = str[i];

        if (!letters[chr]) letters[chr] = 0;

        letters[chr]++;

    }

​

    var halfStr = "";

    for (i in letters) {

        if (letters[i] % 2 !== 0) return 0;

        letters[i] /= 2;

        while (letters[i]--) halfStr += i;

    }

​

    var perms = permutations(halfStr);

    for (i = 0; i < perms.length; i++) {

        if (formsShuffle(perms[i], str)) return perms[i];

    }

    return 0;

}