leetcode114.二叉树展开为链表(java)

题目

官方题解好有意思

/**
 * 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 void flatten(TreeNode root) {
        while(root != null){
            //找左子树的最右节点
            //如果不存在左子树
            if(root.left == null){
                root = root.right;
            }else{
                //找到左子树的最右节点
                TreeNode pre = root.left;
                while(pre.right != null){
                    pre = pre.right;
                }
                //该节点的右节点接右子树
                pre.right = root.right;
                // 根节点的右子树更新为左子树
                root.right = root.left;
                // 根节点的左子树记得置空！！！
                root.left = null;
                //根节点指向下一个节点
                root = root.right;
            }
        }

    }
}

结果