Add solution #451

Author: JoshCrozier

solutions/0451-sort-characters-by-frequency.js

@@ -0,0 +1,24 @@
+/**
+ * 451. Sort Characters By Frequency
+ * https://leetcode.com/problems/sort-characters-by-frequency/
+ * Difficulty: Medium
+ *
+ * Given a string, sort it in decreasing order
+ * based on the frequency of characters.
+ */
+
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var frequencySort = function(s) {
+  const map = new Map();
+  s.split('').forEach(char => {
+    map.set(char, map.has(char) ? map.get(char) + 1 : 1);
+  });
+
+  return [...map]
+    .sort((a, b) => b[1] - a[1])
+    .map(entry => entry[0].repeat(entry[1]))
+    .join('');
+};