LC 二叉树的最大深度
2021-05-11 20:21 jetwill 阅读(35) 评论(0) 编辑 收藏 举报https://leetcode-cn.com/leetbook/read/top-interview-questions-easy/xnd69e/
Recursion
/**
* 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) {
return root == null ? 0: Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
}
}
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
#include <algorithm> // std::max
class Solution {
public:
int maxDepth(TreeNode* root) {
return root == nullptr ? 0 : std::max(maxDepth(root->left),maxDepth(root->right)) + 1;
}
};
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
class Solution(object):
def maxDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
return 0 if root == None else max(self.maxDepth(root.left),self.maxDepth(root.right))+1
BFS
/**
* 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;
//创建一个队列
Deque<TreeNode> deque = new LinkedList<>();
deque.push(root);
int count = 0;
while (!deque.isEmpty()) {
//每一层的个数
int size = deque.size();
while (size-- > 0) {
TreeNode cur = deque.pop();
if (cur.left != null)
deque.addLast(cur.left);
if (cur.right != null)
deque.addLast(cur.right);
}
count++;
}
return count;
}
}
DPS
/**
* 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;
//stack记录的是节点,而level中的元素和stack中的元素
//是同时入栈同时出栈,并且level记录的是节点在第几层
Stack<TreeNode> stack = new Stack<>();
Stack<Integer> level = new Stack<>();
stack.push(root);
level.push(1);
int max = 0;
while (!stack.isEmpty()) {
//stack中的元素和level中的元素同时出栈
TreeNode node = stack.pop();
int temp = level.pop();
max = Math.max(temp, max);
if (node.left != null) {
//同时入栈
stack.push(node.left);
level.push(temp + 1);
}
if (node.right != null) {
//同时入栈
stack.push(node.right);
level.push(temp + 1);
}
}
return max;
}
}