【算法刷题day16】Leetcode:104. 二叉树的最大深度、111. 二叉树的最小深度、222.完全二叉树的节点个数

文章目录

- Leetcode 104. 二叉树的最大深度
- - 解题思路
  - 代码
  - 总结
- Leetcode 111. 二叉树的最小深度
- - 解题思路
  - 代码
  - 总结
- Leetcode 222.完全二叉树的节点个数
- - 解题思路
  - 代码
  - 总结

草稿图网站
java的Deque

Leetcode 104. 二叉树的最大深度

题目：104. 二叉树的最大深度
解析：代码随想录解析

解题思路

代码

/*** 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;*     }* }*///递归
class Solution {public int maxDepth(TreeNode root) {if (root == null)return 0;int leftDepth = maxDepth(root.left);int rightDepth = maxDepth(root.right);return Math.max(leftDepth, rightDepth) + 1;}
}//队列，但是时间很慢
class Solution {public int maxDepth(TreeNode root) {int depth = 0;if (root == null)return depth;Queue<TreeNode> queue = new LinkedList<TreeNode>();queue.add(root);while (!queue.isEmpty()) {int size = queue.size();depth++;for (int i = 0; i < size; i++) {TreeNode node = queue.poll();if (node.left != null)  queue.add(node.left);if (node.right != null)  queue.add(node.right);}}return depth;}
}//栈，但是时间很慢

总结

递归没写过

Leetcode 111. 二叉树的最小深度

题目：111. 二叉树的最小深度
解析：代码随想录解析

解题思路

找到第一个叶子节点就可以返回值

代码

/*** 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;*     }* }*/
//递归//队列，层序遍历
class Solution {public int minDepth(TreeNode root) {if (root == null)return 0;int depth = 0;Queue<TreeNode> queue = new LinkedList<TreeNode>();queue.add(root);while(!queue.isEmpty()){int size = queue.size();depth++;for (int i = 0; i < size; i++){TreeNode node = queue.poll();if (node.left == null && node.right == null)return depth;if (node.left != null)  queue.add(node.left);if (node.right != null) queue.add(node.right);}}return depth;}
}//递归
/*** 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;*     }* }*/
//递归
class Solution {public int minDepth(TreeNode root) {if (root == null)return 0;
//        if (root.left == null && root.right == null)
//            return 1;int leftDepth = minDepth(root.left);int rightDepth = minDepth(root.right);leftDepth = leftDepth == 0 ? rightDepth : leftDepth;rightDepth = rightDepth == 0 ? leftDepth : rightDepth;return Math.min(leftDepth, rightDepth) + 1;}
}

总结

暂无

Leetcode 222.完全二叉树的节点个数

题目：222.完全二叉树的节点个数
解析：代码随想录解析

解题思路

遍历

代码

/*** 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;*     }* }*///递归
class Solution {public int countNodes(TreeNode root) {if (root == null)return 0;int leftNum = countNodes(root.left);int rightNum = countNodes(root.right);return 1 + leftNum + rightNum;}
}//遍历
class Solution {public int countNodes(TreeNode root) {int count = 0;if (root == null)return count;Queue<TreeNode> queue = new LinkedList<TreeNode>();queue.add(root);while (!queue.isEmpty()) {int size = queue.size();for (int i = 0; i < size;  i++) {TreeNode node = queue.poll();count++;if (node.left != null)  queue.add(node.left);if (node.right != null) queue.add(node.right);}}return count;}
}