[leetcode]Symmetric Tree

//判断二叉树是否镜面对称，即判断左右子树是否互为镜像
public class Solution {
    public boolean isSymmetric(TreeNode root) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
       if(root == null) return true;
       return isSymmetric(root.left,root.right);
      
    }
//判断两颗树是否互为镜像，同时满足以下三个条件
//1.root值相等
//2.A的左子树和B的右子树互为镜像
//3.A的右子树和B的左子树互为镜像
    public boolean isSymmetric(TreeNode root1,TreeNode root2){
        if(root1 == null&&root2 == null) return true;
        if(root1 == null||root2 == null) return false;
        if(root1.val!=root2.val) return false;
        return isSymmetric(root1.right,root2.left)&&isSymmetric(root1.left,root2.right);
    }
}

 

题2，求一个二叉树的镜像

递归互换左右子树，注意与上题的区别

public  TreeNode createSymmetric(TreeNode root){
		if(root == null) return null;
		TreeNode cloneRoot = new TreeNode(root.value);
		cloneRoot.rchild = createSymmetric(root.lchild);
		cloneRoot.lchild = createSymmetric(root.rchild);
		return cloneRoot;
	}