java刷题--226翻转二叉树

Posted 2021-06-27 Anrys

java刷题--226翻转二叉树

• 题目
• 代码
• 结果

题目

代码

两种方法都要掌握 因为面试时候不准用递归
递归法

    public TreeNode invertTree(TreeNode root) {
        if(root==null) return null;
        TreeNode temp = root.left;
        root.left = root.right;
        root.right = temp;
        invertTree(root.left);
        invertTree(root.right);
        return root;
    }

迭代法

    public TreeNode invertTree(TreeNode root) {	        
    if (root == null) return null;
    Stack<TreeNode> stack = new Stack<>();
    stack.push(root);	        
    while(!stack.isEmpty()) {
        TreeNode node = stack.pop();
        TreeNode left = node.left;
        node.left = node.right;
        node.right = left;           
        if(node.left != null) {
            stack.push(node.left);
        }
        if(node.right != null) {
            stack.push(node.right);
        }
    }
    return root;
 }

结果