Base algorithm

今天介绍几种常见的算法，在面试中或许能派上用场

1.字符串倒转

 //Reverse a string
         public static string Reverse(string ori)
         {
             string MyOri = ori.Trim();
             if(string.IsNullOrEmpty(MyOri))
             {
                 Console.WriteLine("The string you input is null or empty");
                 return null;
             }
             try
             {
                 StringBuilder sb = new StringBuilder(MyOri.Length);
                 if (MyOri.Contains(' '))
                 {
                     string[] Array = MyOri.Split(' ');

                     for (int i = Array.Length - ; i >= ; i--)
                     {
                         sb.Append(Array[i]+' ');
                     }
                 }
                 else
                 {
                     for(int i=MyOri.Length-;i>=;i--)
                     {
                         sb.Append(MyOri[i]);
                     }
                 }
                 return sb.ToString();
             }
             catch (Exception ex)
             {

                 throw new Exception(ex.ToString());
             }

         }

2.获取数值中最大值

 //Find the max value from int array
         public static int FindMax(int[] A)
         {
             int max = A[];
             for(int i=;i<=A.Length-;i++)
             {
                 if(max<A[i])
                 {
                     max = A[i];
                 }
             }
             return max;
         }

3.获取相同元素,从两个数组中.

  //find common element from two int array
         public static List<int> FindCommonElement(int[] A,int[] B)
         {
             int i = ;
             int j = ;
            List<int> a=new List<int> { };
             while(i<A.Length&&j<B.Length)
             {
                 if(A[i]<B[j])
                 {
                     i++;
                 }
                 else if(A[i]==B[j])
                 {
                     a.Add(A[i]);
                     i++;
                     j++;

                 }
                 else if(A[i]>B[j])
                 {
                     j++;
                 }
             }
             return a.ToList();
         }

4.移除两数组中相同元素

 public static List<int> RemoveSameElement(List<int> A, List<int> B)
        {
            List<int> C1 = new List<int>();
            List<int> C2 = new List<int>();
            for (int i = 0; i <=A.Count()-1; i++)
            {
                for (int j = 0; j <=B.Count() - 1; j++)
                {
                    if (A[i] == B[j])
                    {
                        C1.Add(A[i]);
                    }

                }
            }
            foreach(int item in C1)
            {
                A.Remove(item);
            }

            C2 = A.Concat(B).ToList();
            return C2;
        }

5.找到出现次数最多的元素

 //Find the element which appeard most time
         public static int FindElement(int[] A)
         {
             //适用于重复元素连续一起的情况
             //int currentValue = A[0];
             //int counter = 1;
             //for(int i=1;i<A.Length-1;i++)
             //{
             //    if(currentValue==A[i])
             //    {
             //        counter++;
             //    }
             //    else
             //    {
             //        counter--;
             //        if(counter<0)
             //        {
             //            currentValue = A[i];
             //        }
             //    }
             //}
             //return currentValue;

             var res = from n in A
                       group n by n into g
                       orderby g.Count() descending
                       select g;
             var gr = res.First();
             return gr.First();

         }

6.冒泡排序

  //Bubble Sort
         public static int[] BubbleSort(int[] A)
         {
             for(int i=;i<A.Length;i++)
             {
                 for(int j=i+;j<A.Length;j++)
                 {
                     if(A[i]<A[j])
                     {
                         int temp = A[i];
                         A[i] = A[j];
                         A[j] = temp;
                     }
                 }
             }
             return A;
         }

7.数组求和,一句话

 public static int Sum(int[] a, int n)
         {

             return n ==  ?  : Sum(a, n - ) + a[n - ];

         }