代码随想录算法训练营DAY16 | 二叉树 (3)

一、LeetCode 104 二叉树的最大深度

题目链接：104.二叉树的最大深度https://leetcode.cn/problems/maximum-depth-of-binary-tree/

思路：采用后序遍历递归求解。

class Solution {int ans = 0;public int maxDepth(TreeNode root) {if(root == null){return 0;}int left = maxDepth(root.left);int right = maxDepth(root.right);int depth = 1 + Math.max(left,right);return depth;}
}
/*** 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;*     }* }*/

二、LeetCode 111 二叉树的最小深度

题目链接：111.二叉树的最小深度https://leetcode.cn/problems/minimum-depth-of-binary-tree/

思路：左右孩子均为空才是叶子节点，才可以计算深度。

class Solution {public int minDepth(TreeNode root) {if(root == null){return 0;}//左int left = minDepth(root.left);//右int right = minDepth(root.right);//中//左子树为空、右子树不空的情况（非叶子节点）if(root.left == null && root.right != null){return 1 + right;}//右子树为空，左子树不空的情况if(root.left != null && root.right == null){return 1 + left;}return 1 + Math.min(left,right);}
}
/*** 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;*     }* }*/

三、LeetCode 222 完全二叉树的节点个数

题目链接：222.完全二叉树的节点个数https://leetcode.cn/problems/count-complete-tree-nodes/description/

思路：分别计算左右子树节点个数，再相加。

class Solution {public int countNodes(TreeNode root) {if(root == null){return 0;}//分别计算左右子树节点个数 再相加int left = countNodes(root.left);int right = countNodes(root.right);return left + right + 1;}
}
/*** 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;*     }* }*/

四、今日小结

        偷得浮生半日闲~