LeetCode刷题 | 226. 翻转二叉树、101. 对称二叉树

226. 翻转二叉树

/**
 * 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 null;
        }
        invertTree(root.left);
        invertTree(root.right);
        swapChildren(root);
        return root;
    }

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

101. 对称二叉树

/**
 * 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 compare(root.left,root.right);
    }

    public boolean compare(TreeNode left, TreeNode right){
        if(left != null && right == null){
            return false;
        }
        if(left == null && right != null){
            return false;
        }
        if(left == null && right == null){
            return true;
        }
        if(left.val != right.val){
            return false;
        }
        
        boolean compareOutside = compare(left.left,right.right);
        boolean compareInside = compare(left.right,right.left);

        return compareInside && compareOutside;
    }
}