Generate Parentheses

Generate Parentheses.cpp

@@ -0,0 +1,34 @@
+// https://oj.leetcode.com/problems/generate-parentheses/
+
+class Solution {
+    // nr_open/nr_close: # of open/close paranthesis generated
+    void do_generate(vector<string> &ret, string &buf, int nr_open, int nr_close, int n) {
+        if (nr_open + nr_close == 2 * n) {
+            ret.push_back(buf);
+            return;
+        }
+
+        if (nr_open < n) {
+            buf.push_back('(');
+            do_generate(ret, buf, nr_open + 1, nr_close, n);
+            buf.pop_back();
+        }
+        if (nr_open > nr_close) {
+            buf.push_back(')');
+            do_generate(ret, buf, nr_open, nr_close + 1, n);
+            buf.pop_back();
+        }
+    }
+
+public:
+    vector<string> generateParenthesis(int n) {
+        vector<string> ret;
+        if (n <= 0) {
+            return ret;
+        }
+        string buf;
+        do_generate(ret, buf, 0, 0, n);
+
+        return ret;
+    }
+};