常见算法总结



//*********************************//反转字符

Test Date：Console.WriteLine("abcdef")

                    Console.WriteLine(Reverse3("Iam a Girl"));

                    Console.ReadKey();

 

//*********************************

       publicstaticstring Reverse3(string ori)

       {

           ori = ori.Trim();

           if (string.IsNullOrEmpty(ori))

           {

               returnnull;

           }

           try

           {

               StringBuilder Sb =newStringBuilder(ori.Length);

               if (ori.Contains(' '))

               {

                   string[] array =ori.Split(' ');

                   for (int i = array.Length - 1; i>= 0; i--)

                   {

                       Sb.Append(array[i] + ' ');

                   }

               }

               else

               {

                   for (int i = ori.Length - 1; i >=0; i--)

                   {

                       Sb.Append(ori[i]);

                   }

               }

               return Sb.ToString();

           }

           catch (Exception ex)

           {

               thrownewException(ex.ToString());

           }

       }

//*********************************

      publicstaticvoid Reverse(string str)

       {

           string m ="";

           for (int i = str.Length - 1; i>=0; i--)

           {

               m += str[i];

           }

           Console.WriteLine(m);

           Console.ReadKey();

       }

 

       publicstaticstring Reverse1(string str)

       {

           string[] SStr = str.Split(' ');

           string NewStr ="";

           for (int i = SStr.Length-1; i >= 0;i--)

           {

               NewStr += SStr[i]+' ';

           }

           return NewStr;

        }

 

//*********************************最大最小值

#region Max or min in Array

       publicstaticint FindMax(int[] a)

       {

           int max=a[0];

           for (int i = 0; i < a.Length; i++)

           {

               if(a[i]>max)

               {

                   max = a[i];

               }

 

           }

           return max;

       }

       publicstaticint FindMin(int[] a)

       {

           int min=a[0];

           for(int j=0;j<a.Length;j++)

           {

               if(a[j]<min)

               {

                   min=a[j];

               }

           }

           return min;

       }

  #endregion

//*********************************找出数组中出现次数超过一半（出现次数最多）的元素

分析

设置一个当前值和当前值的计数器，初始化当前值为数组首元素，计数器值为1，然后从第二个元素开始遍历整个数组，对于每个被遍历到的值a[i]

1如果a[i]==currentValue，则计数器值加1

2如果a[i] != currentValue， 则计数器值减1，如果计数器值小于0，则更新当前值为a[i]，并将计数器值重置为1

代码

       #regionFind Element

       publicstaticint FindElement(int[] a)

       {

           int curValue = a[0];

           int count = 1;

           for (int i = 1; i < a.Length;++i)

           {

               if (a[i] == curValue)

               {

                   count++;

               }

               else

               {

                   count--;

                   if (count < 0)

                   {

                       curValue = a[i];

                       count = 1;

                   }

               }

           }

           return curValue;

       }

       #endregion

另一个方法是先对数组排序，然后取中间元素即可，因为如果某个元素的个数超过一半，那么数组排序后该元素必定占据数组的中间位置。

//*********************************数组相同元素(先给数组排序再遍历||=||>||<)

TestDate：

int[] A = { 1,2,3,4,5,10,5};

int[] B = { 1,2,3,5,6,7,8,9,10};

Console.WriteLine(FindElement(A,B));

 

#region Find the common element in two array

       publicstaticvoid FindElement(int[] a, int[] b)

       {

           int i = 0;

           int j = 0;

           while(i<a.Length&&j<b.Length)

           {

               if(a[i]<b[j])

               {

                   i++;

               }

               elseif (a[i] == b[j])

               {

                   Console.WriteLine(a[i]);

                   i++;

                   j++;

                   

               }

               elseif(a[i]>b[j])

               {

                  j++;

               }

           }

       }

 #endregion

//*********************************数组求和一句话（递归）

#region Sum of Array

 

       publicstaticint Sum(int[] a, int n)

       {

           return n == 0 ? 0 : Sum(a, n - 1) + a[n - 1];

       }

 

       #endregion

 

//*********************************Bubble排序

#region Sorting

       publicstaticint[] 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;

       }

       #endregion