面试题

今天去面试考官给了下面几个题，随便做了下

有没有更好的算法来实现这些东西呢？有兴趣的朋友可以探讨下

        //1.实现  string.reverse 方法
        private string Reverse(string str)
        {
            string result = string.Empty;
            if (!string.IsNullOrEmpty(str))
            {
                for (int i = str.Length - 1; i >= 0; i--)
                {
                    result += str[i];
                }
            }
            return result;
        }

        //2.实现  string.Split方法
        private string[] Split(string str, char separate)
        {
            string[] result;
            List<string> outPutList = new List<string>();
            string temp = string.Empty;
            for (int i = 0; i < str.Length; i++)
            {
                if (str[i] != separate)
                {
                    temp += str[i];
                }
                else
                {
                    if (temp != string.Empty)
                    {
                        outPutList.Add(temp);
                        temp = string.Empty;
                    }
                }
            }
            if (temp != string.Empty)
                outPutList.Add(temp);
            result = outPutList.ToArray();
            return result;
        }

        //3.实现 string.SubString 方法
        private string SubString(int startPiont, int lenght)
        {
            string inputString = "abcdefghijklmn";
            string result = string.Empty;

            for (int i = startPiont; i < inputString.Length; i++)
            {
                if (i - startPiont >= lenght) break;
                else result += inputString[i];
            }
            return result;
        }

        //4.实现 string.Contains 方法
        private int Contains(string str1, string str2)
        {
            int result = -1;
            if (string.IsNullOrEmpty(str2) || string.IsNullOrEmpty(str1))
            {
                result = -1;
            }
            else
            {
                for (int i = 0; i <= str1.Length - str2.Length; i++)
                {
                    if (str1[i] == str2[0])
                    {
                        int j = 1;
                        for (j = 1; j < str2.Length && j + i < str1.Length; j++)
                        {
                            if (str2[j] != str1[i + j]) break;
                        }
                        if (j == str2.Length)
                            return i;
                    }
                }
            }
            return result;

        }

        class Node
        {
            public int Data { get; set; }
            public Node Next { get; set; }
        }

        //5.单链表排序返回头结点
        private Node Sort(Node list)
        {
            Node head = new Node();
            Node temp1 = new Node();
            Node temp2 = new Node();
            int re = 0;
            temp1 = list;
            while (temp1.Next != null)
            {
                temp2 = temp1;
                while (temp2.Next != null)
                {
                    temp2 = temp2.Next;
                    if (temp1.Data > temp2.Data)
                    {
                        int t = temp1.Data;
                        temp1.Data = temp2.Data;
                        temp2.Data = t;
                    }
                    if (re == 0)
                    {
                        head = temp1; re++;
                    }
                }
                temp1 = temp1.Next;
            }
            return head;
        }

        //6.翻转单链表
        private Node Reverse(Node list)
        {
            Node temp = list;
            Node upNode = null;
            Node next = null;
            while (temp.Next != null)
            {
                next = temp.Next;
                temp.Next = upNode;
                upNode = temp;
                temp = next;
            }
            temp.Next = upNode;
            return temp;
        }

        //7 实现双链表合并有序链表
        Node Merge(Node list1, Node list2)
        { 
            Node head =new Node();
            Node temp1, temp2;
            Node temp3 = null;
            temp1=list1 ;
            temp2 = list2; 
            while (temp1 != null && temp2 != null)
            {
                Node N = new Node();
                if (temp1.Data > temp2.Data)
                {
                    N = temp1;
                    temp1 = temp1.Next;
                }
                else
                {
                    N = temp2;
                    temp2 = temp2.Next;
                }
                //if 
                if (temp3 == null)
                {
                    temp3 = N;
                    head = N;
                }
                else
                {
                    temp3.Next = N;
                    temp3 = temp3.Next;
                }    
            }
            if(temp2!=null )             
            {
                temp3.Next = temp2;
            }
            if (temp1 != null)
            {
                temp3.Next = temp1;
            } 
            return head; 
        }

        private void NodeTest()
        {
            string beforeSort = "排序前：";
            string afterSort = "排序后：";
            string afterReverse = "翻转后：";
            string AfterMerge = "合并后：";
            Random r = new Random();
            Node head1 = new Node() { Data = r.Next(0, 100) };
            Node temp = new Node();
            temp = head1;
            for (int i = 1; i < 10; i++)
            {
                Node n = new Node();
                n.Data = r.Next(0, 100);
                temp.Next = n;
                temp = n;
            }
            OutPutNode(beforeSort, head1);
            head1 = Sort(head1);
            OutPutNode(afterSort, head1);
            head1 = Reverse(head1);
            OutPutNode(afterReverse, head1);
            Node head2 = new Node() { Data = r.Next(0, 100) };
            temp = head2;
            for (int i = 1; i < 5; i++)
            {
                Node n = new Node();
                n.Data = r.Next(0, 100);
                temp.Next = n;
                temp = n;
            }
            OutPutNode(beforeSort, head2);
            head2 = Sort(head2);
            OutPutNode(afterSort, head2);
            head2 = Reverse(head2);
            OutPutNode(afterReverse, head2);
            OutPutNode(AfterMerge, Merge(head1, head2));
        }

        private void OutPutNode(string headStr, Node temp)
        {
            string printstr = string.Empty;
            printstr += headStr;
            while (temp.Next != null)
            {
                printstr += temp.Data.ToString() + " ";
                temp = temp.Next;
            }

            printstr += temp.Data.ToString();
            textBox1.Text += printstr + "
";
            //MessageBox.Show(printstr); 

        }

        private void Form1_Load(object sender, EventArgs e)
        {
            NodeTest();
        }

  

 //双链表合并另一种思路
        Node Merge2(Node list1, Node list2)
        {
            Node head = new Node();
            Node temp = new Node();
            Node node2 = new Node();
            Node current = new Node();
            if (list1.Data > list2.Data)
            {
                current = list1;
                node2 = list2;
            }
            else
            {
                current = list2;
                node2 = list1;
            }
            head = current; 
            while (current.Next != null)
            {
                if (current.Next.Data < node2.Data)
                { 
                    temp  = current.Next;
                    current.Next = node2;
                    node2 = temp;
                }
                else
                { 
                    current = current.Next;
                }
            }
            current.Next = node2;
            return head;
        }