Add solution #784

Author: JoshCrozier

README.md

@@ -144,6 +144,7 @@
 722|[Remove Comments](./0722-remove-comments.js)|Medium|
 733|[Flood Fill](./0733-flood-fill.js)|Easy|
 739|[Daily Temperatures](./0739-daily-temperatures.js)|Medium|
+784|[Letter Case Permutation](./0784-letter-case-permutation.js)|Medium|
 791|[Custom Sort String](./0791-custom-sort-string.js)|Medium|
 796|[Rotate String](./0796-rotate-string.js)|Easy|
 804|[Unique Morse Code Words](./0804-unique-morse-code-words.js)|Easy|

solutions/0784-letter-case-permutation.js

@@ -0,0 +1,35 @@
+/**
+ * 784. Letter Case Permutation
+ * https://leetcode.com/problems/letter-case-permutation/
+ * Difficulty: Medium
+ *
+ * Given a string s, you can transform every letter individually to be lowercase or uppercase
+ * to create another string.
+ *
+ * Return a list of all possible strings we could create. Return the output in any order.
+ */
+
+/**
+ * @param {string} str
+ * @return {string[]}
+ */
+var letterCasePermutation = function(str) {
+  const result = [];
+  backtrack(result, str);
+  return result;
+};
+
+function backtrack(result, input, permutation = '', offset = 0) {
+  if (input.length === permutation.length) {
+    result.push(permutation);
+  } else {
+    const target = input[offset];
+    if (isNaN(target)) {
+      [target.toLowerCase(), target.toUpperCase()].forEach(s => {
+        backtrack(result, input, permutation + s, offset + 1);
+      });
+    } else {
+      backtrack(result, input, permutation + target, offset + 1);
+    }
+  }
+}