（半转载）Sunday算法（字符串完全匹配）

http://www.cnblogs.com/lbsong/archive/2012/05/25/2518188.html

比KMP更容易理解的sunday算法，O(m+n)，不用计算next数组，比KMP更快。

A = "LESSONS TEARNED IN SOFTWARE TE";

B = "SOFTWARE";

先从左到右逐个字符比较，以我们的字符串为例：

开始的时候，我们让i = 0, 指向A的第一个字符; j = 0 指向B的第一个字符，分别为"L"和"S"，不等；这个时候，Sunday算法要求，找到位于A字串中位于B字符串后面的第一个字符，即T。 从后向前遍历B串，找到相等的字母。将B串移至使T对齐的地方，如第二步。继续从B的开头比较，重复第一步和第二步，直至找到，或者A遍历结束。如果A字符串后位于B字符串后面的第一个字符T在B中没有对应的字符，就将整个B串与T之后的字符对齐。

第一步：

LESSONS TEARNED IN SOFTWARE TE

SOFTWARE

第二步：

LESSONS TEARNED IN SOFTWARE TE

         SOFTWARE

int  sunday( char  *w,  char  *t)

{

                  if  (strlen(t)>strlen(w))

                                  return  -1;

                  int  i1,i2;

                  int  prei;

                  int  i,j;

                  int  index;

                i1 = 0;

                i2 = 0;

                index = -1;

                  while  (i1<strlen(w)){

                                prei = i1;

                                  for  (i2 = 0;i2<strlen(t)&&i1<strlen(w);++i2,++i1)

                                                  if  (w[i1] != t[i2])

                                                                  break  ;

                                  if  (i2 == strlen(t)){

                                                index = prei;

                                                  break  ;

                                }

                                i = prei + strlen(t);

                                  if  (i == strlen(w))

                                                  break  ;

                                  for  (j=strlen(t)-1;j>=0;--j)

                                                  if  (t[j] == w[i])

                                                                  break  ;

                                  if  (j >= 0)

                                                i1 = i-j;

                                  else

                                                i1 = i+1;

                }

                  return  index;

}