add: 字符串解码

test/stack/decode-string.test.js

@@ -0,0 +1,7 @@
+import { decodeString } from '../../src/stack/decode-string'
+
+test('字符串解码', () => {
+  expect(decodeString('3[a]2[bc]')).toBe('aaabcbc')
+  expect(decodeString('3[a2[c]]')).toBe('accaccacc')
+  expect(decodeString('2[abc]3[cd]ef')).toBe('abcabccdcdcdef')
+})