代码随想录四刷day15

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文章目录

前言
[一、力扣100. 相同的树](#一、力扣100. 相同的树)
[二、力扣572. 另一棵树的子树](#二、力扣572. 另一棵树的子树)
[三、力扣104. 二叉树的最大深度](#三、力扣104. 二叉树的最大深度)
[四、力扣559. N 叉树的最大深度](#四、力扣559. N 叉树的最大深度)

前言

最小深度是从根节点到最近叶子节点的最短路径上的节点数量。

一、力扣100. 相同的树

递归

java 复制代码

/**
 * 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 boolean isSameTree(TreeNode p, TreeNode q) {
        return fun(p,q);
    }
    public boolean fun(TreeNode p, TreeNode q){
        if(p == null && q == null){
            return true;
        }
        if(p == null || q == null){
            return false;
        }
        if(p.val != q.val){
            return false;
        }
        boolean b1 = fun(p.left, q.left);
        boolean b2 = fun(p.right,q.right);
        return b1 && b2;
    }
}

迭代

java 复制代码

/**
 * 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 boolean isSameTree(TreeNode p, TreeNode q) {
        Deque<TreeNode> deq = new LinkedList<>();
        deq.offerLast(p);
        deq.offerLast(q);
        while(!deq.isEmpty()){
            TreeNode t1 = deq.pollFirst();
            TreeNode t2 = deq.pollFirst();
            if(t1 == null && t2 == null){
                continue;
            }
            if(t1 == null || t2 == null){
                return false;
            }
            if(t1.val != t2.val){
                return false;
            }
            deq.offerLast(t1.left);
            deq.offerLast(t2.left);
            deq.offerLast(t1.right);
            deq.offerLast(t2.right);
        }
        return true;
    }
}

二、力扣572. 另一棵树的子树

java 复制代码

/**
 * 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 boolean isSubtree(TreeNode root, TreeNode subRoot) {
        return postOrder(root,subRoot);
    }
    public boolean postOrder(TreeNode root, TreeNode subRoot){
        if(root == null){
            return false;
        }
        boolean b1 = postOrder(root.left,subRoot);
        if(b1){
            return b1;
        }
        boolean b2 = postOrder(root.right,subRoot);
        if(b2){
            return b2;
        }
        boolean b3 = fun(root,subRoot);
        return b1 || b2 || b3;
    }
    public boolean fun(TreeNode p, TreeNode q){
        if(p == null && q == null){
            return true;
        }
        if(p == null || q == null){
            return false;
        }
        if(p.val != q.val){
            return false;
        }
        boolean b1 = fun(p.left,q.left);
        boolean b2 = fun(p.right,q.right);
        return b1 && b2;
    }
}

三、力扣104. 二叉树的最大深度

java 复制代码

/**
 * 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) {
        return fun(root);
    }
    public int fun(TreeNode root){
        if(root == null){
            return 0;
        }
        int l = fun(root.left);
        int r = fun(root.right);
        return l > r ? l + 1 : r + 1;
    }
}

四、力扣559. N 叉树的最大深度

java 复制代码

/*
// 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) {
        return fun(root);
    }
    public int fun(Node root){
        if(root == null){
            return 0;
        }
        int max = 0;
        for(Node node : root.children){
            max = Math.max(max,fun(node));
        }
        return max + 1;
    }
}