代码随想录Day12 二叉树 LeetCode T102二叉树的层序遍历 T226 翻转二叉树 T101 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 {
    List<List<Integer>> result = new ArrayList<>();
    public List<List<Integer>> levelOrder(TreeNode root) {
        CheckOrder(root);
        return result;
    }
     public void  CheckOrder(TreeNode node)
     {
        if(node == null)
        {
            return;
        }
        Queue<TreeNode> que = new LinkedList<>();
        que.offer(node);
        while(!que.isEmpty())
        {
            List<Integer> tmp = new ArrayList<>();
            int size = que.size();
            while(size>0)
            {
                TreeNode tmpNode = que.poll();
                tmp.add(tmpNode.val);
                if(tmpNode.left != null)
                {
                    que.offer(tmpNode.left);
                }
                if(tmpNode.right != null)
                {
                    que.offer(tmpNode.right);
                }
                size--;
            }
            result.add(tmp);
        }
     }
}

TreeNode invertTree(TreeNode root)

if(root == null)
    {
        return root;
    }

Swap(root);
        invertTree(root.left);
        invertTree(root.right);

/**
 * 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 tmp = root.left;
        root.left = root.right;
        root.right = tmp;
    }
}

/**
 * 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 cmp(root.left,root.right);
    }
    boolean cmp(TreeNode left,TreeNode right)
    {
        if(left==null &&right != null)
        {
            return false;
        }
        else if(left != null && right == null)
        {
            return false;
        }
        else if(left == null && right == null)
        {
            return true;
        }
        else if(right.val !=left.val)
        {
            return false;
        }
        boolean outSide = cmp(left.left,right.right);
        boolean inSide = cmp(left.right,right.left);
        return outSide && inSide;
    }
}