代码随想录算法刷题训练营day15

代码随想录算法刷题训练营day15：LeetCode(226)翻转二叉树、LeetCode(101)对称二叉树

LeetCode(226)翻转二叉树
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 TreeNode invertTree(TreeNode root) {
        if(root==null){
            return root;
        }
        swap(root);
        invertTree(root.left);
        invertTree(root.right);
        return root;

    }
    public void swap(TreeNode root){
        TreeNode temp=root.left;
        root.left=root.right;
        root.right=temp;
    }
}

LeetCode(101)对称二叉树
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 boolean isSymmetric(TreeNode root) {
        //做一个交换的递归
        boolean result=compare(root.left,root.right);
        return result;

    }
    public boolean compare(TreeNode left,TreeNode right){
        if(left==null&&right==null){
            return true;
        }else if(left!=null&&right==null){
            return false;
        }else if(left==null&&right!=null){
            return false;
        }else if(left!=null&&right!=null&&left.val!=right.val){
            return false;
        }else{
            //两个节点对称----考虑比较外侧和内测的元素
            //比较外侧
            boolean result1=compare(left.left, right.right);
            //比较内测
            boolean result2=compare(left.right, right.left);
            return result1&&result2;
        }
    }
}