递归解决

- 完全二叉树：子树就是一个个满二叉树
- 平衡二叉树：递归求高度，用-1判断是否平衡

src/main/java/cn/whaifree/leetCode/Tree/LeetCode110.java

@@ -0,0 +1,48 @@
+package cn.whaifree.leetCode.Tree;
+
+import cn.whaifree.leetCode.model.TreeNode;
+import org.junit.Test;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/1/21 20:36
+ * @注释
+ */
+public class LeetCode110 {
+
+    @Test
+    public void test() {
+        TreeNode treeNode = TreeNode.constructTree(new Integer[]{1,2,2,3,null,null,3,4,null,null,4});
+        treeNode.printTree();
+        System.out.println(new Solution().isBalanced(treeNode));
+    }
+
+    class Solution {
+        public boolean isBalanced(TreeNode root) {
+            return level(root)!=-1;
+        }
+
+        public int level(TreeNode root) {
+            if (root == null) {
+                return 0;
+            }
+            int leftHeight = level(root.left);
+            if (leftHeight == -1) {
+                return -1;
+            }
+            int rightDepth = level(root.right);
+            if (rightDepth == -1) {
+                return -1;
+            }
+            if (Math.abs(leftHeight - rightDepth) > 1) {
+                return -1;
+            }
+            return Math.max(leftHeight, rightDepth) + 1;
+//            return Math.abs(leftHeight - rightDepth) > 1 ? -1 : Math.max(leftHeight, rightDepth) + 1;
+        }
+    }
+}

src/main/java/cn/whaifree/leetCode/Tree/LeetCode222.java

@@ -0,0 +1,73 @@
+package cn.whaifree.leetCode.Tree;
+
+import cn.whaifree.leetCode.model.TreeNode;
+import org.junit.Test;
+
+/**
+ * @version 1.0
+ * @Author whai文海
+ * @Date 2024/1/22 19:05
+ * @注释
+ */
+public class LeetCode222 {
+
+    @Test
+    public void test() {
+        TreeNode treeNode = TreeNode.constructTree(new Integer[]{1, 2, 3, 4, 5, 6});
+        treeNode.printTree();
+        System.out.println(new Solution1().countNodes(treeNode));
+    }
+
+    class Solution {
+
+
+        public int countNodes(TreeNode root) {
+            return inLevel(root);
+        }
+
+        public int inLevel(TreeNode node) {
+            if (node==null) return 0;
+            int left = inLevel(node.left) + 1;
+            int right = inLevel(node.right) ;
+            return left + right;
+        }
+    }
+
+    class Solution1 {
+
+
+        public int countNodes(TreeNode root) {
+            return inLevel(root);
+        }
+
+        public int inLevel(TreeNode node) {
+            if (node == null) {
+                return 0;
+            }
+            // 计算左边深度
+            int leftDepth = 0;
+            TreeNode leftNode = node.left;
+            while (leftNode != null) {
+                leftNode = leftNode.left;
+                leftDepth++;
+            }
+
+            // 计算右边深度
+            int rightDepth = 0;
+            TreeNode rightNode = node.right;
+            while (rightNode != null) {
+                rightNode = rightNode.right;
+                rightDepth++;
+            }
+
+            // 如果两变深度一样，那么该树是完全二叉树
+            if (leftDepth == rightDepth) {
+                return (2 << leftDepth) - 1;
+            }
+            // 如果两边深度不一样，递归左右子节点+1
+            return inLevel(node.right) + inLevel(node.left) + 1;
+
+        }
+    }
+
+}