generate parentheses

Author: zgpeace

code/LeetCode/src/backtracking/GenerateParentheses.java

@@ -0,0 +1,41 @@
+package backtracking;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+// https://leetcode.com/problems/generate-parentheses/
+public class GenerateParentheses {
+
+  public static void main(String[] args) {
+    GenerateParentheses obj = new GenerateParentheses();
+    List<String> result = obj.generateParenthesis(3);
+    System.out.println("result > " + Arrays.toString(result.toArray()));
+  }
+
+  public List<String> generateParenthesis(int n) {
+    List<String> result = new ArrayList<>();
+    if (n <= 0) {
+      return result;
+    }
+
+    helper(result, "", n, n);
+
+    return result;
+  }
+
+  public void helper(List<String> result, String combine, int left, int right) {
+    //exit
+    if (left == 0 && right == 0) {
+      result.add(combine);
+      return;
+    }
+
+    if (left > 0) {
+      helper(result, combine + '(', left - 1, right);
+    }
+    if (right > left) {
+      helper(result, combine + ')', left, right - 1);
+    }
+  }
+}