Add: Exercise 394. Decode String

Author: BlackBeast593

394-decode-string/README.md

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+# 394. Decode String
+Given an encoded string, return its decoded string.
+
+The encoding rule is: `k[encoded_string]`, where the `encoded_string` inside the square brackets is
+being repeated exactly `k` times. Note that `k` is guaranteed to be a positive integer.
+
+You may assume that the input string is always valid; there are no extra white spaces, square
+brackets are well-formed, etc. Furthermore, you may assume that the original data does not contain
+any digits and that digits are only for those repeat numbers, `k`. For example, there will not be
+input like `3a` or `2[4]`.
+
+The test cases are generated so that the length of the output will never exceed 10^5.
+
+## Examples
+
+### Example 1:
+
+Input: `s` = "3[a]2[bc]"  
+Output: "aaabcbc"  
+Explanation: The string "3[a]2[bc]" is decoded as "aaabcbc".
+
+### Example 2:
+
+Input: `s` = "3[a2[c]]"  
+Output: "accaccacc"  
+Explanation: The string "3[a2[c]]" is decoded as "accaccacc".
+
+### Example 3:
+
+Input: `s` = "2[abc]3[cd]ef"  
+Output: "abcabccdcdcdef"  
+Explanation: The string "2[abc]3[cd]ef" is decoded as "abcabccdcdcdef".
+
+## Constraints
+
+- 1 <= `s.length` <= 30
+- `s` consists of lowercase English letters, digits, and square brackets `'[]'`.
+- `s` is guaranteed to be a valid input.
+- All the integers in `s` are in the range [1, 300].

394-decode-string/index.js

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+/**
+ * 
+ * @param {*} s 
+ * @returns 
+ */
+const decodeString = s => {
+    const stack = []
+    stack.peek = () => stack[stack.length - 1]
+
+    for (let c of s) {
+        // Everything will be pushed to stack, until a ']' char is found
+        if (c !== ']') {
+            stack.push(c)
+            continue
+        }
+
+        // ']' found, let's obtain the substring that will be multiplied and added to the stack
+        let subStr = ''
+        while (stack.peek() !== '[') {
+            subStr = stack.pop() + subStr
+        }
+
+        // Eliminate '[' from the stack before to proceed
+        stack.pop()
+
+        // '[' found, let's obtain the multiplier
+        let multiplierStr = ''
+        while (!Number.isNaN(Number(stack.peek()))) {
+            multiplierStr = stack.pop() + multiplierStr
+        }
+
+        const multiplier = Number(multiplierStr)
+
+        // Now let's muliply add the str to the stack
+        for (let i = 0; i < multiplier; i++) {
+            stack.push(subStr)
+        }
+    }
+
+    delete stack.peek
+
+    return stack.join('')
+};
+
+var output = decodeString('3[a]2[bc]')
+
+module.exports = decodeString

394-decode-string/package.json

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+{
+  "name": "394-decode-string",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js",
+    "debug": "node --inspect-brk index.js",
+    "test": "node test.js"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC"
+}

394-decode-string/test.js

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+const assert = require('assert')
+const decodeString = require('./index')
+
+const tests = [
+    {
+        s: '3[a]2[bc]',
+        output: 'aaabcbc'
+    },
+    {
+        s: '3[a2[c]]',
+        output: 'accaccacc'
+    },
+    {
+        s: '2[abc]3[cd]ef',
+        output: 'abcabccdcdcdef'
+    }
+]
+
+for (const t of tests) {
+    assert(decodeString(t.s), t.output)
+}