897. 递增顺序查找树

题目描述已经给出了解法：中序遍历（左根右），如果要就地更新原树其实还是有些麻烦的，但如果中序遍历后新建一个数就很简单了。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    List<int> list = new List<int>();
    public TreeNode IncreasingBST(TreeNode root) {
        if(root == null)
            return root;
        func(root);

        TreeNode ts = new TreeNode(0);
        TreeNode t = new TreeNode(list[0]);
        ts.right = t;
        for(int i = 1;i < list.Count(); i++)
        {
            t.right = new TreeNode(list[i]);
            t = t.right;
        }
        return ts.right;
    }
    public void func(TreeNode t)
    {
        if(t == null)
            return;
        func(t.left);
        list.Add(t.val);
        func(t.right);

    }
}