二叉树遍历、深度、直径

Author: haotf

Diff for: 104.二叉树的最大深度.java

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+/*
+ * @lc app=leetcode.cn id=104 lang=java
+ *
+ * [104] 二叉树的最大深度
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode() {}
+ * TreeNode(int val) { this.val = val; }
+ * TreeNode(int val, TreeNode left, TreeNode right) {
+ * this.val = val;
+ * this.left = left;
+ * this.right = right;
+ * }
+ * }
+ */
+class Solution {
+    public int maxDepth(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
+    }
+}
+// @lc code=end

Diff for: 144.二叉树的前序遍历.java

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+import java.util.ArrayList;
+import java.util.List;
+
+/*
+ * @lc app=leetcode.cn id=144 lang=java
+ *
+ * [144] 二叉树的前序遍历
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode() {}
+ * TreeNode(int val) { this.val = val; }
+ * TreeNode(int val, TreeNode left, TreeNode right) {
+ * this.val = val;
+ * this.left = left;
+ * this.right = right;
+ * }
+ * }
+ */
+class Solution {
+    public List<Integer> preorderTraversal(TreeNode root) {
+        List<Integer> list = new ArrayList<Integer>();
+        if (root == null) {
+            return list;
+        }
+
+        list.add(root.val);
+        list.addAll(preorderTraversal(root.left));
+        list.addAll(preorderTraversal(root.right));
+        return list;
+    }
+}
+// @lc code=end

Diff for: 226.翻转二叉树.java

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+/*
+ * @lc app=leetcode.cn id=226 lang=java
+ *
+ * [226] 翻转二叉树
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode() {}
+ * TreeNode(int val) { this.val = val; }
+ * TreeNode(int val, TreeNode left, TreeNode right) {
+ * this.val = val;
+ * this.left = left;
+ * this.right = right;
+ * }
+ * }
+ */
+class Solution {
+    public TreeNode invertTree(TreeNode root) {
+        if (root == null)
+            return null;
+        TreeNode tmp = root.left;
+        root.left = root.right;
+        root.right = tmp;
+        invertTree(root.left);
+        invertTree(root.right);
+        return root;
+    }
+}
+// @lc code=end

Diff for: 543.二叉树的直径.java

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+/*
+ * @lc app=leetcode.cn id=543 lang=java
+ *
+ * [543] 二叉树的直径
+ */
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ * int val;
+ * TreeNode left;
+ * TreeNode right;
+ * TreeNode() {}
+ * TreeNode(int val) { this.val = val; }
+ * TreeNode(int val, TreeNode left, TreeNode right) {
+ * this.val = val;
+ * this.left = left;
+ * this.right = right;
+ * }
+ * }
+ */
+class Solution {
+    private int maxDiameter = 0;
+
+    public int diameterOfBinaryTree(TreeNode root) {
+        traverse(root);
+        return maxDiameter;
+    }
+
+    private int traverse(TreeNode root) {
+        if (root == null) {
+            return 0;
+        }
+        // 计算左右子树高度
+        int left = traverse(root.left);
+        int right = traverse(root.right);
+        // 更新最大直径
+        maxDiameter = Math.max(left + right, maxDiameter);
+
+        return 1 + Math.max(left, right);
+    }
+}
+// @lc code=end

Diff for: TreeNode.java

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+public class TreeNode {
+    int val;
+    TreeNode left;
+    TreeNode right;
+
+    TreeNode() {
+    }
+
+    TreeNode(int val) {
+        this.val = val;
+    }
+
+    TreeNode(int val, TreeNode left, TreeNode right) {
+        this.val = val;
+        this.left = left;
+        this.right = right;
+    }
+}