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 - 1; i >= 0; i--)
                    {
                        sb.Append(Array[i]+' ');
                    }
                }
                else
                {
                    for(int i=MyOri.Length-1;i>=0;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[0];
            for(int i=1;i<=A.Length-1;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 = 0;
            int j = 0;
           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=0;i<A.Length;i++)
            {
                for(int j=i+1;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 == 0 ? 0 : Sum(a, n - 1) + a[n - 1];

        }