我自己写的divide&conquer

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    /**     * @param root: The root of binary tree.     * @return: An integer.     */    public int maxDepth(TreeNode root) {        // write your code here        if (root == null) {            return 0;  //?        }        int result = divide(root);        return result;    }    private int divide(TreeNode root) {        if (root == null) {            return 0;        }        int re1 = divide(root.left);        int re2 = divide(root.right);        if (re1 >= re2) {            return re1 + 1;        } else {            return re2 +1;        }    }}

九章

// Version 1: Divide Conquerpublic class Solution {    public int maxDepth(TreeNode root) {        if (root == null) {            return 0;        }        int left = maxDepth(root.left);        int right = maxDepth(root.right);        return Math.max(left, right) + 1;    }}

递归老写错，摊手╮(╯-╰)╭

正确的：我抄的答案

/*** Definition of TreeNode:* public class TreeNode {* public int val;* public TreeNode left, right;* public TreeNode(int val) {* this.val = val;* this.left = this.right = null;* }* }*/public class Solution {/*** @param root: The root of binary tree.* @return: An integer.*/    private int result;    public int maxDepth(TreeNode root) {    // write your code here        result = 0;   //这里不能写int result 不能重新定义        traverse(root, 1);//传入1不是0        return result;    }    private void traverse(TreeNode root, int curr) {        if (root == null) {        return ;        }                if (curr > result) { //先写这个            result = curr;        }        traverse(root.left, curr + 1);        traverse(root.right, curr + 1);    }}

九章

// version 2: Traverse/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    /**     * @param root: The root of binary tree.     * @return: An integer.     */    private int depth;        public int maxDepth(TreeNode root) {        depth = 0;        helper(root, 1);                return depth;    }        private void helper(TreeNode node, int curtDepth) {        if (node == null) {            return;        }                if (curtDepth > depth) {            depth = curtDepth;        }                helper(node.left, curtDepth + 1);        helper(node.right, curtDepth + 1);    }}

错的

/**

* Definition of TreeNode:

* public class TreeNode {

* public int val;

* public TreeNode left, right;

* public TreeNode(int val) {

* this.val = val;

* this.left = this.right = null;

* }

* }

*/

public class Solution {

/**

* @param root: The root of binary tree.

* @return: An integer.

*/

public int maxDepth(TreeNode root) {

// write your code here

if (root == null) {

return 0; //?

}

int result = 0;

traverse(root, result);

return result;

}

private void traverse(TreeNode root, int result) {

if (root == null) {

return;

}

int re1 = 0;

int re2 = 0;

traverse(root.left, re1);

traverse(root.right, re2);

if (re1 >= re2) {

result = re1 + 1;

} else {

result = re2 +1;

}

}

}