再次完成110

docs/0000-21-dynamic-programming.adoc

@@ -12,6 +12,7 @@ include::0000-21-dp-4-palindromic-subsequence.adoc[leveloffset=+1]
 include::0000-21-dp-5-longest-common-substring.adoc[leveloffset=+1]
 
 
+[#tree-dp-trick]
 == 树形 DP 套路
 
 树形 DP 套路使用前提：如果题目求解目标是 S 规则，则求解释流程可以定成以每一个节点为头节点的子树在 S 规则下的每一个答案，并且最终答案一定就在其中。

docs/0110-balanced-binary-tree.adoc

@@ -1,3 +1,4 @@
+[#0110-balanced-binary-tree]
 = 110. Balanced Binary Tree
 
 https://leetcode.com/problems/balanced-binary-tree/[LeetCode - Balanced Binary Tree]
@@ -55,7 +56,7 @@ Return false.
 
 == 参考资料
 
-. https://leetcode-cn.com/problems/balanced-binary-tree/solution/balanced-binary-tree-di-gui-fang-fa-by-jin40789108/[Balanced Binary Tree （Top-down和Bottom-up递归方法） - 平衡二叉树 - 力扣（LeetCode）]
+. https://leetcode.cn/problems/balanced-binary-tree/solutions/8737/balanced-binary-tree-di-gui-fang-fa-by-jin40789108/[Balanced Binary Tree （Top-down和Bottom-up递归方法） - 平衡二叉树 - 力扣（LeetCode）]
 
 
 [[src-0110]]
@@ -64,3 +65,21 @@ Return false.
 include::{sourcedir}/_0110_BalancedBinaryTree.java[]
 ----
 
+== 基于树形 DP 套路解法
+
+这个解法参考了：xref:0000-21-dynamic-programming.adoc[动态规划] 中介绍的 “树形 DP 套路” 解法。
+
+[{java_src_attr}]
+----
+include::{sourcedir}/_0110_BalancedBinaryTree_2.java[]
+----
+
+== 剪枝优化后的解法
+
+参考论坛中大家的讨论，可以在发现不平衡时，就及时返回，停止执行其他相关递归调用，起到“剪枝”的作用。同时，时间复杂度也可以做到最好。
+
+[{java_src_attr}]
+----
+include::{sourcedir}/_0110_BalancedBinaryTree_21.java[]
+----
+

src/main/java/com/diguage/algorithm/leetcode/_0110_BalancedBinaryTree_2.java

@@ -0,0 +1,53 @@
+package com.diguage.algorithm.leetcode;
+
+import com.diguage.algorithm.util.TreeNode;
+
+import java.util.Objects;
+
+import static com.diguage.algorithm.util.TreeNodeUtils.buildTree;
+import static java.util.Arrays.asList;
+
+/**
+ * = 110. Balanced Binary Tree
+ *
+ * https://leetcode.com/problems/balanced-binary-tree/[LeetCode - Balanced Binary Tree]
+ *
+ * @author D瓜哥, https://www.diguage.com/
+ * @since 2020-02-06 23:10
+ */
+public class _0110_BalancedBinaryTree_2 {
+
+  /**
+   * 使用“树形 DP 套路”
+   */
+  public boolean isBalanced(TreeNode root) {
+    return dfs(root).balance;
+  }
+
+  public Record dfs(TreeNode root) {
+    if (root == null) {
+      return new Record(true, 0);
+    }
+    Record left = dfs(root.left);
+    Record right = dfs(root.right);
+    boolean balance = left.balance && right.balance && Math.abs(left.height - right.height) <= 1;
+    return new Record(balance, Math.max(left.height, right.height) + 1);
+  }
+
+  public static class Record {
+    public boolean balance;
+    public int height;
+
+    public Record(boolean balance, int height) {
+      this.balance = balance;
+      this.height = height;
+    }
+  }
+
+  public static void main(String[] args) {
+    _0110_BalancedBinaryTree_2 solution = new _0110_BalancedBinaryTree_2();
+    System.out.println(!solution.isBalanced(buildTree(asList(1, 2, 2, 3, null, null, 3, 4, null, null, 4))));
+    System.out.println(solution.isBalanced(buildTree(asList(3, 9, 20, null, null, 15, 7))));
+    System.out.println(!solution.isBalanced(buildTree(asList(1, 2, 2, 3, 3, null, null, 4, 4))));
+  }
+}

src/main/java/com/diguage/algorithm/leetcode/_0110_BalancedBinaryTree_21.java

@@ -0,0 +1,48 @@
+package com.diguage.algorithm.leetcode;
+
+import com.diguage.algorithm.util.TreeNode;
+
+import static com.diguage.algorithm.util.TreeNodeUtils.buildTree;
+import static java.util.Arrays.asList;
+
+/**
+ * = 110. Balanced Binary Tree
+ *
+ * https://leetcode.com/problems/balanced-binary-tree/[LeetCode - Balanced Binary Tree]
+ *
+ * @author D瓜哥, https://www.diguage.com/
+ * @since 2020-02-06 23:10
+ */
+public class _0110_BalancedBinaryTree_21 {
+
+  /**
+   * 看了论坛中大家的讨论，做了提前结束递归的优化。
+   */
+  public boolean isBalanced(TreeNode root) {
+    return dfs(root) >= 0;
+  }
+
+  public int dfs(TreeNode root) {
+    if (root == null) {
+      return 0;
+    }
+    int left = dfs(root.left);
+    // 发现不平衡即提前结束递归
+    if (left < 0) {
+      return -1;
+    }
+    int right = dfs(root.right);
+    // 发现不平衡即提前结束递归
+    if (right < 0) {
+      return -1;
+    }
+    return Math.abs(left - right) > 1 ? -1 : Math.max(left, right) + 1;
+  }
+
+  public static void main(String[] args) {
+    _0110_BalancedBinaryTree_21 solution = new _0110_BalancedBinaryTree_21();
+    System.out.println(!solution.isBalanced(buildTree(asList(1, 2, 2, 3, null, null, 3, 4, null, null, 4))));
+    System.out.println(solution.isBalanced(buildTree(asList(3, 9, 20, null, null, 15, 7))));
+    System.out.println(!solution.isBalanced(buildTree(asList(1, 2, 2, 3, 3, null, null, 4, 4))));
+  }
+}