二叉树展开为链表

代码：

class Solution {
    public void flatten(TreeNode root) {
        TreeNode curr = root;
        while (curr != null) {
            if (curr.left!=null){
                TreeNode left = curr.left;
                TreeNode temp = left;
                //找到左子树最右边的节点
                while(temp.right!=null){
                    temp = temp.right;
                }
                //将整个右子树全部拼接到左子树的最右节点
                temp.right=curr.right;
                //将左子树转变到右子树
                curr.left=null;
                curr.right=left;
            }
            curr = curr.right;
        }
    }
}
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;
    }
}