[22] 括号生成

src/leecode/22.括号生成.java

@@ -0,0 +1,52 @@
+package leecode;/*
+ * @lc app=leetcode.cn id=22 lang=java
+ *
+ * [22] 括号生成
+ */
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Stack;
+
+// @lc code=start
+class No22 {
+    public List<String> generateParenthesis(int n) {
+        Stack<String> stack = new Stack<>();
+        List<String> result = new ArrayList<>();
+        boolean selectLeft = true;
+        StringBuilder create = new StringBuilder();
+        select(stack, result, n-1, n, selectLeft, create.append("("));
+        return result;
+    }
+
+    private void select(Stack<String> stack, List<String> result, int left, int right, boolean selectLeft, StringBuilder create) {
+        if (left == 0 && right == 0) {
+            if (stack.isEmpty() || !stack.pop().equals("(")) {
+                return;
+            }
+            result.add(create.toString());
+            return;
+        }
+        if (left < 0 || right < 0) {
+            return;
+        }
+        if (selectLeft) {
+            stack.push("(");
+        } else {
+            if (stack.isEmpty() || !stack.pop().equals("(")) {
+                return;
+            }
+        }
+        select((Stack<String>) stack.clone(), result, left - 1, right, true, create.append("("));
+        create.delete(create.length() - 1, create.length());
+        select((Stack<String>) stack.clone(), result, left, right-1, false, create.append(")"));
+        create.delete(create.length() - 1, create.length());
+    }
+
+    public static void main(String[] args) {
+        No22 solution = new No22();
+        System.out.println(solution.generateParenthesis(2));
+    }
+}
+// @lc code=end
+