394. Decode String (axross#142)

Author: Kohei Asai

Diff for: solutions/decode_string.ts

@@ -0,0 +1,33 @@
+// 394. Decode String
+// https://leetcode.com/problems/decode-string/
+export default function decodeString(s: string): string {
+  let decoded = "";
+  let repeat = 0;
+  let brackets = 0;
+  let bracketFrom = 0;
+
+  for (let i = 0; i < s.length; ++i) {
+    if (s[i] === "[") {
+      brackets += 1;
+
+      if (brackets === 1) {
+        bracketFrom = i;
+      }
+    } else if (s[i] === "]") {
+      brackets -= 1;
+
+      if (brackets === 0) {
+        decoded += decodeString(s.substring(bracketFrom + 1, i)).repeat(repeat);
+        repeat = 0;
+      }
+    } else if (brackets === 0) {
+      if (s.charCodeAt(i) >= 48 && s.charCodeAt(i) <= 57) {
+        repeat = repeat * 10 + s.charCodeAt(i) - 48;
+      } else {
+        decoded += s[i];
+      }
+    }
+  }
+
+  return decoded;
+}

Diff for: solutions/decode_string_test.ts

@@ -0,0 +1,13 @@
+import { test } from "https://deno.land/std/testing/mod.ts";
+import { assertStrictEq } from "https://deno.land/std/testing/asserts.ts";
+import decodeString from "./decode_string.ts";
+
+test("394. Decode String", () => {
+  assertStrictEq(decodeString("3[a]2[bc]"), "aaabcbc");
+  assertStrictEq(decodeString("3[a2[c]]"), "accaccacc");
+  assertStrictEq(decodeString("2[abc]3[cd]ef"), "abcabccdcdcdef");
+  assertStrictEq(
+    decodeString("a2[b3[c4[d]e]]f3[g]h"),
+    "abcddddecddddecddddebcddddecddddecddddefgggh"
+  );
+});