update: 779

Author: hijiangtao

README.md

@@ -144,3 +144,4 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |523|[Continuous Subarray Sum](https://leetcode.com/problems/continuous-subarray-sum/) | [JavaScript](./src/continuous-subarray-sum/res.js)|Medium|
 |539|[Minimum Time Difference](https://leetcode.com/problems/minimum-time-difference/) | [JavaScript](./src/minimum-time-difference/res.js)|Medium|
 |687|[Longest Univalue Path](https://leetcode.com/problems/longest-univalue-path/) | [JavaScript](./src/longest-univalue-path/res.js)|Easy|
+|779|[K-th Symbol in Grammar](https://leetcode.com/problems/k-th-symbol-in-grammar/) | [JavaScript](./src/k-th-symbol-in-grammar/res.js)|Medium|

src/k-th-symbol-in-grammar/res.js

@@ -0,0 +1,17 @@
+/**
+* @param {number} N
+* @param {number} K
+* @return {number}
+*/
+var kthGrammar = function(N, K) {
+if (N === 1) return 0;
+if (N === 2) return K - 1;
+
+const index = Math.pow(2, N - 1);
+
+if (K <= index / 2) {
+return kthGrammar(N - 1, K);
+} else {
+return 1 - kthGrammar(N - 1, K - index / 2);
+}
+};