Merge pull request #202 from c99SRS/beta

added parenthesis qns

Author: kaal-coder

Coding/GenerateParentheses.java

@@ -0,0 +1,67 @@
+/*
+Generate Parentheses
+
+Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
+
+ 
+
+Example 1:
+
+Input: n = 3
+Output: ["((()))","(()())","(())()","()(())","()()()"]
+
+Example 2:
+
+Input: n = 1
+Output: ["()"]
+
+ 
+
+Constraints:
+1 <= n <= 8
+
+*/
+
+class Solution {
+    
+    List<String> ansList = new ArrayList();
+    public List<String> generateParenthesis(int n) {
+        
+        StringBuilder curr = new StringBuilder();
+        
+        
+        generate(curr,0,0,n);
+        
+        return ansList;
+    }
+    
+    void generate(StringBuilder curr,int openCount,int closedCount, int n){
+    
+        
+         if(openCount == n && closedCount == n){
+            ansList.add(curr.toString());
+            return;
+        }
+        
+         if(openCount > n || closedCount > n)
+             return;
+
+        
+        // choice 1
+          if(openCount < n){
+            curr.append("(");
+            generate(curr, openCount+1, closedCount, n);
+            curr.deleteCharAt(curr.length()-1);
+          }
+        
+        // choice 2
+         if(openCount > closedCount){
+            curr.append(")");
+            generate(curr, openCount, closedCount+1, n);
+            curr.deleteCharAt(curr.length()-1);
+        } 
+        
+        return;
+    }
+    
+ }