力扣算法题简单（六）

1. 653. 两数之和 IV - 输入 BST

 public List<int> Go(TreeNode root)
    {
        List<int> list = new List<int>();
        if (root == null) return list;
        list.AddRange(Go(root?.left));
        list.Add(root.val);
        list.AddRange(Go(root?.right));
        return list;
    }
    public bool FindTarget(TreeNode root, int k)
    {
        List<int> list = Go(root);
        for (int i = 0; i < list.Count; i++)
        {
            for (int j = i + 1; j < list.Count; j++)
            {
                if (list[i] + list[j] == k)
                {
                    return true;
                }
            }
        }
        return false;
    }

2. 191. 位1的个数

    public int HammingWeight(uint n)
    {
        string k = Convert.ToString(n, 2);
        return k.Where(item => item == '1').Count();
    }