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;
    }
}