[LeetCode] 101. Symmetric Tree (Easy)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34

구현을 못해서 힌트 받고 품
/**
 * 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) {
        return checkSymmetric(root.left, root.right);
    }

    boolean checkSymmetric(TreeNode left, TreeNode right){
        if(left == null && right != null) return false;
        if(right == null && left != null) return false;
        if(right == null && left == null) return true;
        
        if(left.val != right.val) return false;

        if(checkSymmetric(left.left, right.right) == false) return false;
        if(checkSymmetric(left.right, right.left) == false) return false;
        
        return true;
    }
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18

class Solution {
    public boolean isSymmetric(TreeNode root) {
        if (root == null) {
            return true;
        }
        return isMirror(root.left, root.right);
    }
    
    private boolean isMirror(TreeNode node1, TreeNode node2) {
        if (node1 == null && node2 == null) {
            return true;
        }
        if (node1 == null || node2 == null) {
            return false;
        }
        return node1.val == node2.val && isMirror(node1.left, node2.right) && isMirror(node1.right, node2.left);
    }
}