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Author: 17tanya

Backtracking/GenerateParentheses.java

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+//LeetCode 22. Generate Parentheses
+//Question - https://leetcode.com/problems/generate-parentheses/
+
+class Solution {
+    public List<String> generateParenthesis(int n) {
+        List<String> res = new ArrayList<>();
+        helper("", res, 0, 0, n);
+        return res;
+    }
+    
+    public void helper(String str, List<String> l, int open, int close, int n){
+        if(str.length() == n*2){
+            l.add(str);
+            return;
+        }
+        
+        //each valid parentheses must have n open braces and not more.
+        if(open < n) helper(str + '(', l, open + 1, close, n);
+        //To maintain a valid parentheses, the closed brackets can only be added when 
+        //we have corresponding open brackets available.
+        if(close < open) helper(str + ')', l, open, close + 1, n);
+    }
+}