Add solution #791

Author: JoshCrozier

solutions/0791-custom-sort-string.js

@@ -0,0 +1,26 @@
+/**
+ * 791. Custom Sort String
+ * https://leetcode.com/problems/custom-sort-string/
+ * Difficulty: Medium
+ *
+ * S and T are strings composed of lowercase letters. In S,
+ * no letter occurs more than once.
+ *
+ * S was sorted in some custom order previously. We want to
+ * permute the characters of T so that they match the order
+ * that S was sorted. More specifically, if x occurs before
+ * y in S, then x should occur before y in the returned string.
+ *
+ * Return any permutation of T (as a string) that satisfies
+ * this property.
+ */
+
+/**
+ * @param {string} S
+ * @param {string} T
+ * @return {string}
+ */
+var customSortString = function(S, T) {
+  const order = S.split('').reduce((o, k, i) => ({...o, [k]: i}), {});
+  return T.split('').sort((a, b) => (order[a] || 0) - (order[b] || 0)).join('');
+};