LeetCode热题100道-Day07

101. 对称二叉树

• 使用递归，如果左树的左子树与右树的右子树对称，左树的右子树与右树的左子树对称，那么这个左树和右树就对称。

/**
 * 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) {
        if (root == null){
            return false;
        }

        return check(root.left,root.right);
    }

    public boolean check(TreeNode left, TreeNode right){
        if(left == null || right == null){
            return left == right;
        }
        if(left.val != right.val){
            return false;
        }
        return check(left.left,right.right) && check(left.right,right.left);
    }
}

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isSymmetric(root *TreeNode) bool {
    if root == nil {
        return false
    }
    return check(root.Left,root.Right)
}

func check(left *TreeNode, right *TreeNode) bool{
    if left == nil || right == nil {
        return left == right
    }
    if left.Val != right.Val {
        return false
    }
    return check(left.Left , right.Right ) && check(left.Right , right.Left )
}