Add BF optimized solution for generating the paranthesis.

anxious-coder-lhs · anxious-coder-lhs · commit 1e8dcbd12d42 · 2020-10-14T23:05:35.000+05:30
diff --git a/README.md b/README.md
@@ -51,7 +51,7 @@ Happy to accept any contributions to this in any langugage.
 16. [LeetCode Web Crawler 1242](https://leetcode.com/problems/web-crawler-multithreaded/) | [Solution 1 ](./level_medium/LeetCode_WebCrawler_MultiThreaded_1242.java) | [Solution 2](level_medium/LeetCode_WebCrawler_MultiThreaded_1242_1.java)
 17. [Leet Code 554 Brick Wall](https://leetcode.com/problems/brick-wall/) | [Solution 1](./level_medium/LeetCode_554_Brick_Wall_Medium.ts)
 18. [Leet Code 1190 Reverse Substrings Between Each Pair of Paranthesis](https://leetcode.com/problems/reverse-substrings-between-each-pair-of-parentheses/) | [Solution 1](level_medium/LeetCode_1190_Reverse_Substrings.ts) | [Solution Optimized](level_medium/LeetCode_1190_Reverse_Substrings_1.ts)
-19. [Leet Code 22 Generate Paranthesis](https://leetcode.com/problems/generate-parentheses/) | [Solution Brute Force](level_medium/LeetCode_22_Generate_Paranthesis_1.ts)
+19. [Leet Code 22 Generate Paranthesis](https://leetcode.com/problems/generate-parentheses/) | [Solution Brute Force](level_medium/LeetCode_22_Generate_Paranthesis_1.ts) | [Solution BF Optimized](level_medium/LeetCode_22_Generate_Paranthesis_2.ts)
 
 
 ## Hard
diff --git a/level_medium/LeetCode_22_Generate_Paranthesis_2.ts b/level_medium/LeetCode_22_Generate_Paranthesis_2.ts
@@ -0,0 +1,41 @@
+/**
+ * Leverages the permutation solution as discussed in the last solution. However, the solution
+ * also leverages some optimization where the the validity of the solution is checked along while
+ * building the solutions, rather than the running an operation of O(n) later to complete the validation.
+ * 
+ * Complexity: Time: O(2^n) time complexity for generating all possible pairs.
+ * Space: O(2^n) for the entire solution space.
+ * 
+ * @param n 
+ */
+function generateParenthesis(n: number): string[] {
+    return generateParanthesisHelper(n * 2)
+};
+
+function generateParanthesisHelper(n: number, curr: number = 0, result: string[] = [], braces: number = 0): string[] {
+        
+    const output: string[] = [];
+    
+    if (curr >= n) {
+        // Done for all the positions, validate the created string.
+        if (braces === 0)
+            output.push(result.join(""))
+
+        return output;
+    }
+    
+    // At the position curr, choose one of the braces and recursively move.
+    result[curr] = "("
+    output.push(...generateParanthesisHelper(n, curr + 1, result, braces + 1));
+    
+    // At the position curr, choose one of the braces and recursively move.
+    if (braces >= 1) {
+        
+        // Only make this choice, if it won't make the string valid.
+        result[curr] = ")"
+        output.push(...generateParanthesisHelper(n, curr + 1, result, braces - 1));    
+    }
+    
+    // Return the final results.
+    return output;
+}
