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代码随想录算法刷题训练营day16：LeetCode(104)二叉树的最大深度 、LeetCode(559)n叉树的最大深度、LeetCode(111)二叉树的最小深度、LeetCode(222)完全二叉树的节点个数

LeetCode(104)二叉树的最大深度
题目

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;*     }* }*/
class Solution {public int maxDepth(TreeNode root) {//通过递归去做---传入的是根节点，可以求根节点的高度来代替深度//先求左右子树的高度+1即为根节点的高度----确定遍历方式为左右根//采用递归，先判断终止条件if(root==null){return 0;}//不为空，先求左子树的高度int heightLeft=maxDepth(root.left);//再求右子树的高度int heightRight=maxDepth(root.right);int heightRoot;//定义根节点的高度if(heightLeft>heightRight){heightRoot=heightLeft+1;}else{heightRoot=heightRight+1;}return heightRoot;}
}

LeetCode(559)n叉树的最大深度
题目

代码

// @lc code=start
/*
// Definition for a Node.
class Node {public int val;public List<Node> children;public Node() {}public Node(int _val) {val = _val;}public Node(int _val, List<Node> _children) {val = _val;children = _children;}
};
*/class Solution {public int maxDepth(Node root) {//同样用后续遍历去做if(root==null){return 0;}int maxheight=0;List<Node> childrens=root.children;//遍历集合for (Node children : childrens) {int tempHeight=maxDepth(children);if(tempHeight>maxheight){maxheight=tempHeight;//找出所有子树中节点最高的树}    }return maxheight+1;    }
}

LeetCode(111)二叉树的最小深度
题目

代码

// @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 minDepth(TreeNode root) {if(root==null){return 0;}int rootHeight;//同样用后续遍历去做if(root.left==null){rootHeight=minDepth(root.right)+1;return rootHeight;}if(root.right==null){rootHeight=minDepth(root.left)+1;return rootHeight;}int leftHeight=minDepth(root.left);int rightHeight=minDepth(root.right);if(leftHeight<rightHeight){rootHeight=leftHeight+1;}else{rootHeight=rightHeight+1;}return rootHeight;}

LeetCode(222)完全二叉树的节点个数
题目

代码

// @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 {int number=0;public int countNodes(TreeNode root) {if(root==null){return 0;}int leftCountNodes=countNodes(root.left);int rightCountNodes=countNodes(root.right);int countSum=leftCountNodes+rightCountNodes+1;//常规遍历方法return countSum;}
}