Add solutions to q 148

Author: logreg-n-coffee

code/148-generate-gray-code.ts

@@ -0,0 +1,34 @@
+/*
+Gray code is a binary code where each successive value differ 
+in only one bit, as well as when wrapping around. 
+Gray code is common in hardware so that we don't see temporary spurious values during transitions.
+
+Given a number of bits n, generate a possible gray code for it.
+
+For example, for n = 2, one gray code would be [00, 01, 11, 10].
+
+https://en.wikipedia.org/wiki/Gray_code
+ */
+
+// use recursion to solve gray code problem
+(() => { 
+    function grayCode(n: number): number[] {
+        if (n === 0) return [];
+        else if (n === 1) return [0, 1];
+
+        const prevGrayCode = grayCode(n - 1);
+        const result = [];
+
+        for (const code of prevGrayCode) {
+            result.push(code);
+        }
+
+        for (const code of prevGrayCode.reverse()) {
+            result.push((1 << n - 1) + code);
+        }
+
+        return result;
+    }
+
+    console.log(grayCode(2).map(x => x.toString(2)));
+})();

package.json

@@ -149,7 +149,8 @@
     "144": "nodemon --exec ts-node code/144-nearest-larger-number.ts",
     "145": "nodemon --exec ts-node code/145-swap-every-two-nodes-linked-list.ts",
     "146": "nodemon --exec ts-node code/146-prune-a-tree.ts",
-    "147": "nodemon --exec ts-node code/147-sort-a-list-using-reverse.ts"
+    "147": "nodemon --exec ts-node code/147-sort-a-list-using-reverse.ts",
+    "148": "nodemon --exec ts-node code/148-generate-gray-code.ts"
   },
   "keywords": [],
   "author": "",