C#:算法题

1. 将字符串s1中所有出现在字符串s2中的字符删去

 using System;

 namespace ConsoleApplication56
 {
     class Program
     {
         static void Main(string[] args)
         {
             string s1 = "aaabbccabfcabcc";
             string s2 = "abcd";
 
             char[] results = new char[s1.Length];
             int m=0;
             int j, i;
             for (i = 0; i < s1.Length; i++)
             {
                 for (j=0; j < s2.Length; j++)
                 {
                     if (s1[i] != s2[j])
                     {
                         continue;
                     }
                     else
                     {
                         j = 0;
                         break;
                     }
                 }
                 if (j == s2.Length)
                 {
                     results[m++] = s1[i];
                 }
             }
 
             foreach (char a in results)
             {
                 Console.WriteLine(a.ToString());
             }
             Console.ReadLine();
         }
     }
 }

2. 计算数字出现次数(using LinkedList)

using System;
using System.Collections.Generic;

namespace ConsoleApplication57
{
    class Program
    {

        static void Main(string[] args)
        {
            int[] nums = { 1, 2, 3, 4, 2, 1 };
            int count = 0;

            if (nums != null)
            {
                LinkedList<int> numbers = new LinkedList<int>(nums);
                int givenInt = 1;

                LinkedListNode<int> currentNode = numbers.First;
                while (currentNode != null)
                {
                    if (currentNode.Value == givenInt)
                    {
                        count++;
                    }
                    currentNode = currentNode.Next;
                }
            }

            Console.WriteLine(count);
            Console.ReadLine();
        }
    }
}

3.I have two strings the ending substring of first is the starting substring of the second,ex

string left : ONESTRING
string right : STRINGTWO

I have to merge them so that the resulting string is

result string : ONESTRINGTWO

using System;

namespace ConsoleApplication58
{
    class Program
    {
        static void Main(string[] args)
        {
            string left = "OneStart";
            string right = "StartTwo";
            string result = FindAndMerge(left, right);
            Console.WriteLine(result);
            Console.ReadLine();
        }

        public static string FindAndMerge(string left,string right)
        {
            int i=0;
            string result=string.Empty;

            for (i = right.Length; i >= 0; i--)
            {
                if (left.Contains(right.Substring(0, i)))
                {
                    break;
                }
            }

            if (i < right.Length)
            {
                result = right.Substring(i);
            }

            result = left + result;
            return result;
        }
    }
}

4. 删除重复元素

using System;

namespace ConsoleApplication41
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Please input the size of the int Array:");
            int size = Int32.Parse(Console.ReadLine());
            int[] array = new int[size];
            Console.WriteLine("Please input {0} numbers:", size);

            if (size > 0)
            {
                for (int i = 0; i < size; i++)
                {
                    array[i] = GetInputNum();
                }

                int[] result = DelDupElements(array);
                foreach (int i in result)
                {
                    Console.WriteLine(i);
                }
            }
            else
            {
                Console.WriteLine("Please input new array with more than zero numbers");
            }
            Console.ReadLine();
        }

        /// <summary>
        /// 
        /// </summary>
        /// <returns></returns>
        public static int GetInputNum()
        {
            try
            {
                return Int32.Parse(Console.ReadLine());
            }
            catch
            {
                Console.WriteLine("Please input a number");
                return GetInputNum();
            }
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="a"></param>
        /// <returns></returns>
        public static int[] DelDupElements(int[] a)
        {
            // Special judgement

            if (a.Length == 0)
            {
                Console.WriteLine("Please input new array with more than zero numbers");
                return null;
            }

            else
            {
                // Sort the array
                Sort(a);
                Console.WriteLine("The sorted array:");
                foreach (int i in a)
                {
                    Console.WriteLine(i);
                }
                Console.ReadLine();

                int[] resultArrary;
                int j = 1;
                int size = 1;
                for (int i = 1; i < a.Length; i++)
                {
                    if (a[i] != a[i - 1])
                    {
                        size++;
                    }
                }
                resultArrary = new int[size];
                resultArrary[0] = a[0];
                for (int i = 1; i < a.Length; i++)
                {
                    if (a[i] != a[i - 1])
                    {
                        resultArrary[j++] = a[i];
                    }
                }
                return resultArrary;
            }
        }

        /// <summary>
        /// 
        /// </summary>
        /// <param name="a"></param>
        public static void Sort(int[] a)
        {
            int temp;
            for (int i = 1; i < a.Length; i++)
            {
                for (int j = 0; j < a.Length - i; j++)
                {
                    if (a[j] > a[j + 1])
                    {
                        temp = a[j];
                        a[j] = a[j + 1];
                        a[j + 1] = temp;
                    }
                }
            }
        }
    }
}

另外几种种写法：

public static void DeleteDuplicateNumbers(int[] array)
        {
            if (array != null)
            {
                List<int> result = new List<int>();
                if (array.Length > 1)
                {
                    for (int i = 0; i < array.Length; i++)
                    {
                        if (!result.Contains(array[i]))
                        {
                            result.Add(array[i]);
                        }
                    }
                }
                else
                {
                    result.Add(array[0]);
                }
                foreach (int i in result)
                {
                    Console.WriteLine(i);
                }
                Console.ReadLine();
            }
        }

public static void DeleteDuplicateNumbersUsingIndexOf(int[] array)
        {
            if (array != null)
            {
                List<int> result = new List<int>();
                if (array.Length > 1)
                {
                    for (int i = 0; i < array.Length; i++)
                    {
                        if (result.IndexOf(array[i]) < 0)
                        {
                            result.Add(array[i]);
                        }
                    }
                }
                else
                {
                    result.Add(array[0]);
                }
                foreach (int i in result)
                {
                    Console.WriteLine(i);
                }
                Console.ReadLine();
            }
            else
            {
                Console.WriteLine("The array is null");
            }
        }

        public static void DeleteDuplicateNumbersUsingInsert(int[] array)
        {
            if (array != null)
            {
                List<int> result = new List<int>();
                result.Add(array[0]);
                if (array.Length > 1)
                {
                    for (int i = 1; i < array.Length; i++)
                    {
                        if (array[i] < result[0])
                        {
                            result.Insert(0, array[i]);
                        }
                        else if (array[i] > result[result.Count - 1])
                        {
                            result.Add(array[i]);
                        }
                        else
                        {
                            for (int j = 1; j < result.Count-1; j++)
                            {
                                if (array[i] > result[j-1] && array[i] < result[j])
                                {
                                    result.Insert(j, array[i]);
                                }
                            }
                        }
                    }
                }
                foreach (int i in result)
                {
                    Console.WriteLine(i);
                }
                Console.ReadLine();
            }
        }

        public static int[] DeleteDuplicateNumbersUsingArrayList(int[] list)
        {
            ArrayList arr = new ArrayList();
            for (int i = 0; i < list.Length - 1; i++)
            {
                if (list[i] != list[i + 1])
                {
                    arr.Add(list[i]);
                }
            }
            arr.Add(list[list.Length - 1]);
            int[] getarr = new int[arr.Count];
            for (int i = 0; i < arr.Count; i++)
            {
                getarr[i] = Convert.ToInt32(arr[i]);
            }

            return getarr;
        }

5. 合并有序数组

using System;

namespace ConsoleApplication62
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] a = { 1, 2, 2, 3, 5, 6, 7, 7 };
            int[] b = { 1, 2, 3, 4, 8, 8, 9, 10, 11, 12, 12, 13, 14 };
            int[] c = MergeList(a, b);
            foreach (int i in c)
            {
                Console.WriteLine(i);
            }
            Console.ReadLine();
        }

        public static int[] MergeList(int[] a, int[] b)
        {
            if (checkSort(a) && checkSort(b))
            {
                int len = a.Length + b.Length;
                int[] result = new int[len];

                int i = 0, j = 0, k = 0;
                while (i < a.Length && j < b.Length)
                {
                    if (a[i] < b[j])
                    {
                        result[k++] = a[i++];
                    }
                    else
                    {
                        result[k++] = b[j++];
                    }
                }

                while (i < a.Length)
                {
                    result[k++] = a[i++];
                }
                while (j < b.Length)
                {
                    result[k++] = b[j++];
                }

                return result;
            }
            else
            {
                return null;
            }

        }

        public static bool checkSort(int[] a)
        {
            for (int i = 0; i < a.Length - 1; i++)
            {
                for (int j = i + 1; j < a.Length; j++)
                {
                    if (a[j - 1] > a[j])
                    {
                        return false;
                    }
                }
            }
            return true;
        }
    }
}

 6. 有一列数1，1，2，3，5，........求第30个数.

public class MainClass
    {
        public static void Main()
        {
            Console.WriteLine(Foo(12));
            Console.ReadLine();
        }

        public static int Foo(int i)
        {
            if (i <= 0)
                return 0;
            else if (i > 0 && i <= 2)
                return 1;
            else return Foo(i - 1) + Foo(i - 2);
        }
    }

7. 冒泡排序、选择排序、插入排序

   // 冒泡排序 bubble sort
        public static int[] BubbleSort(int[] array)
        {
            int temp;
            bool isDone = false;
            for (int i = 0; i < array.Length && !isDone; i++)
            {
                isDone = true;
                for (int j = 0; j < array.Length - i - 1; j++)
                {
                    if (array[j] > array[j + 1])
                    {
                        isDone = false;
                        temp = array[j];
                        array[j] = array[j + 1];
                        array[j + 1] = temp;
                    }
                }
            }
                return array;
        }

// 插入排序 Insertion sort
        public static int[] InsertionSort(int[] array)
        {
            for (int i = 1; i < array.Length; i++)
            {
                int current = array[i];
                int j = i;
                while (j > 0 && current < array[j - 1])
                {
                    array[j] = array[j - 1];
                    j--;
                }
                array[j] = current;
            }

            return array;
        }

// 选择排序 Selection sort
        public static int[] SelectionSort(int[] array)
        {
            for (int i = 0; i < array.Length; i++)
            {
                int min = i;
                for (int j = i + 1; j < array.Length; j++)
                {
                    if (array[j] < array[min])
                    {
                        min = j;
                    }
                }
                int temp = array[i];
                array[i] = array[min];
                array[min] = temp;
            }

            return array;
        }

8. 找第二大的数

// 获得数组中的第二大数
        public static int SecondMax(int[] array)
        {
            int max = array[0];
            int secondMax = array[0];
            for (int i = 0; i < array.Length; i++)
            {
                if (array[i] > max)
                {
                    secondMax = max;
                    max = array[i];
                }
                else if (array[i] > secondMax && array[i] != max)
                {
                    secondMax = array[i];
                }
            }

            if (secondMax == max)
            {
                throw new Exception("Have no second max!");
            }

            return secondMax;
        }

9. 有一个字符串 "I am a good man",设计一个函数,返回 "man good a am I"

// 反转单词顺序
        public static string WordReverse(string str)
        {
            char[] array = str.ToArray();
            CharArrayReverse(array, 0, array.Length - 1);
            int start = -1;
            int end = -1;
            for (int i = 0; i < array.Length; i++)
            {
                if (!((array[i] >= 'a' && array[i] <= 'z') || (array[i] >= 'A' && array[i] <= 'Z')))
                {
                    if (start < end)
                    {
                        CharArrayReverse(array, start + 1, end);
                    }
                    start = i;
                }
                else
                {
                    end = i;
                }
            }
            return new string(array);
        }

        public static void CharArrayReverse(char[] array, int start, int end)
        {
            if (array != null && start < array.Length && end < array.Length)
                while (start < end)
                {
                    char temp = array[start];
                    array[start] = array[end];
                    array[end] = temp;
                    start++;
                    end--;
                }
        }

10.  Ａ、Ｂ、Ｃ、Ｄ、Ｅ五名学生有可能参加计算机竞赛，根据下列条件判断哪些   人参加了竞赛：

   （１）Ａ参加时，Ｂ也参加；

   （２）Ｂ和Ｃ只有一个人参加；

   （３）Ｃ和Ｄ或者都参加，或者都不参加；

   （４）Ｄ和Ｅ中至少有一个人参加；

   （５）如果Ｅ参加，那么Ａ和Ｄ也都参加。

public static void Main()
        {
            char[] name = { 'A', 'B', 'C', 'D', 'E' };
            int[] value = new int[5];
            for (value[0] = 0; value[0] < 2; value[0]++)
            {
                for (value[1] = 0; value[1] < 2; value[1]++)
                {
                    for (value[2] = 0; value[2] < 2; value[2]++)
                    {
                        for (value[3] = 0; value[3] < 2; value[3]++)
                        {
                            for (value[4] = 0; value[4] < 2; value[4]++)
                            {
                                if ((value[1] >= value[0]) && (value[1] + value[2] == 1) && (value[2] == value[3]) && (value[3] + value[4] == 1) && (value[4] == 0 || value[4] == 1 && value[0] == 1 && value[3] == 1))
                                {
                                    for (int i = 0; i < 5; i++)
                                    {
                                        if (value[i] == 1)
                                        {
                                            Console.WriteLine("{0}Join", name[i]);
                                        }
                                        else
                                        {
                                            Console.WriteLine("{0}Not Join", name[i]);
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
                Console.ReadLine();
        }

11. a user entered an integer value into a text box. Without using a buit-in library, convert the numeric string to its integer representation.

        public static int StringToInt(string s)
        {
            int sum = 0;
            for (int i = 0; i < s.Length; i++)
            {
                sum = sum * 10 + (s[i] - '0');
            }
            return sum;

        }