scramble-string.js

/**
 * @param {string} s1
 * @param {string} s2
 * @return {boolean}
 */

var isScramble = function(s1, s2) {

    return helper({}, s1, s2);
};

var helper = function (dp, s1, s2) {
  var map = {};

  if (dp[s1 + s2] !== undefined) return dp[s1 + s2];
  if (s1 === s2) return true;

  for (var j = 0; j < s1.length; j++) {
    if (map[s1[j]] === undefined) map[s1[j]] = 0;
    if (map[s2[j]] === undefined) map[s2[j]] = 0;
    map[s1[j]]++;
    map[s2[j]]--;
  }

  for (var key in map) {
    if (map[key] !== 0) {
      dp[s1 + s2] = false;
      return false;
    }
  }

  for (var i = 1; i < s1.length; i++) {
    if ((helper(dp, s1.substr(0, i), s2.substr(0, i))
         && helper(dp, s1.substr(i), s2.substr(i))) ||
        (helper(dp, s1.substr(0, i), s2.substr(s2.length - i))
         && helper(dp, s1.substr(i), s2.substr(0, s2.length - i)))) {
      dp[s1 + s2] = true;
      return true;
    }
  }

  dp[s1 + s2] = false;
  return false;
};