LeetCode之653. Two Sum IV - Input is a BST

* 这题属于Two Sum题，将BST中根遍历存到数组当中，转换为数组的Two Sum问题即可 *

C # 代码

public bool FindTarget(TreeNode root, int k)
        {
            List<int> lst = new List<int>();
            BST2Lst(root,ref lst);
            int i = 0;
            int j = lst.Count-1;
            while(i<j)
            {
                if(lst[i] + lst[j] == k)
                {
                    return true;
                }
                if( lst[i]+lst[j] < k)
                    i++;
                else 
                    j--;
            }

            return false;


        }
        public  void  BST2Lst(TreeNode root, ref List<int> lst)
        {
            if(root == null)
                return ;

            BST2Lst(root.left, ref lst);
            lst.Add(root.val);
            BST2Lst(root.right, ref lst);

        }

python 3代码

class Solution:
    def findTarget(self, root, k):
        """
        :type root: TreeNode
        :type k: int
        :rtype: bool
        """
        lst = []
        self.BST2Lst(root, lst)
        i = 0
        j = len(lst)-1
        while(i<j):
            flag = lst[i]+lst[j]
            if flag == k :
                return True
            if flag < k:
                i += 1
            else:
                j -= 1
        return False

    def BST2Lst(self, root, lst):
        if root == None:
            return
        self.BST2Lst(root.left, lst)
        lst.append(root.val)
        self.BST2Lst(root.right, lst)