LeetCode第669题 修剪二叉搜索树

1. 算法
   深度优先搜索
2. 核心思想
   主要还是如何减枝比较重要。
3. 代码

class Solution {
    public TreeNode trimBST(TreeNode root, int low, int high) {
        if (root == null) return null;

        if(root.val > high || root.val < low) {
            root = del(root);
            root = trimBST(root,low,high);
        }else{
            root.right = trimBST(root.right, low, high);
            root.left = trimBST(root.left, low, high);
        }


        return root;
    }

    private TreeNode del(TreeNode root) {
        if (root.left == null)   return root.right;
        else if (root.right == null)  return root.left;
        else if (root.left!=null && root.right !=null){
            TreeNode node = root.right;
            while (node.left != null)
                node = node.left;

            node.left = root.left;
            root = root.right;
        }
        return root;
    }

}