串的模式匹配算法之二:首尾匹配算法

using System;
namespace EasyIndex
{
    class Index
    {
        static void Main(string[] args)
        {
            string s="acabaabcaabaabcac";
            string m="abaabcac";
            int i=0;
            int j=0;
            while(i<s.Length && j<m.Length)
            {
                if(s[i]==m[0])//判断两串的第一个元素是否相等
                {
                    if(s[i+m.Length-1]==m[m.Length-1])//如果头元素相等,再判断尾元素是否相等;
                    {
                        i=1;
                        j=0;
                        while(i<s.Length && j<m.Length)//如果头尾都相等,再从第二个元素到倒数第二个元素判断;
                        {
                            if(s[i]==m[j])
                            {
                                i++;
                                j++;
                            }
                            else
                            {
                                i=i-j+1;
                                j=0;
                            }
                        }
                    }
                    else
                    {
                        i=i-j+1;
                        j=0;
                    }
                }
                else
                {
                    i=i-j+1;
                    j=0;
                }
              }
            if(j>=m.Length)//说明m是s的一个子串,而且pos是i-m.Lengh+1,因为数组从0开始计数;
            {
                Console.WriteLine("m与s中第"+Convert.ToString(i-m.Length+1)+"个元素开始的子串相匹配!");
            }
            else
            {
                Console.WriteLine("m不是s的子串!");
            }

        }
    }
}