187th Commit

README.md

@@ -143,10 +143,11 @@ Ace Coding Interview with 75 Qs
 | ---------------------------------- | ---------------- | ------ |
 | 2390. Removing Stars From a String | [Solution][2390] | Medium |
 | 735. Asteroid Collision            | [Solution][735]  | Medium |
-| 394. Decode String                 | Solution         | Medium |
+| 394. Decode String                 | [Solution][394]  | Medium |
 
 [2390]: ./src/page-22/2390.%20Removing%20Stars%20From%20a%20String/removeStars.ts
 [735]: ./src/page-7/735.%20Asteroid%20Collision/asteroidCollision.ts
+[394]: ./src/page-4/394.%20Decode%20String/decodeString.ts
 
 | Queue                       |          |        |
 | --------------------------- | -------- | ------ |

src/page-4/394. Decode String/decodeString.test.ts

@@ -0,0 +1,9 @@
+import { decodeString } from './decodeString';
+
+describe('394. Decode String', () => {
+  test('decodeString', () => {
+    expect(decodeString('3[a]2[bc]')).toBe('aaabcbc');
+    expect(decodeString('3[a2[c]]')).toBe('accaccacc');
+    expect(decodeString('2[abc]3[cd]ef')).toBe('abcabccdcdcdef');
+  });
+});

src/page-4/394. Decode String/decodeString.ts

@@ -0,0 +1,36 @@
+type DecodeString = (s: string) => string;
+
+/**
+ * Accepted
+ */
+export const decodeString: DecodeString = (s) => {
+  const countStack: number[] = []; // Stack to store repeat counts
+  const stringStack: string[] = []; // Stack to store intermediate strings
+
+  let currentNum = 0; // Current number being processed
+  let currentString = ''; // Current string being processed
+
+  for (const char of s) {
+    if (!Number.isNaN(Number(char))) {
+      // If the character is a digit, update currentNum
+      currentNum = currentNum * 10 + Number(char);
+    } else if (char === '[') {
+      // If the character is '[', push currentNum and currentString to stacks
+      countStack.push(currentNum);
+      stringStack.push(currentString);
+      currentNum = 0; // Reset currentNum
+      currentString = ''; // Reset currentString
+    } else if (char === ']') {
+      // If the character is ']', pop from stacks and update currentString
+      const repeatTimes = countStack.pop(); // Get the last count
+      const lastString = stringStack.pop(); // Get the last string
+      currentString = lastString + currentString.repeat(repeatTimes || 1); // Repeat currentString and append
+    } else {
+      // If the character is a letter, append it to currentString
+      currentString += char;
+    }
+  }
+
+  // Return the fully decoded string
+  return currentString;
+};