填空题

[说明] 若s和t是用单链表存储的两个串，设计一个函数将s串中首次与串t匹配的字串逆置。
linkstring * invert - substring ( s, t)
linkstring * s, * t;
linkstring *prior, *p, *t1, *r, *q, *u;
prior =s;
p=s;
t1 =t;
if ( (1) ) printf ( "error\n") ;
else

while p ! = NULL && t1! = NULL)

if ( p- ＞data = = t1 - ＞data)

p = p- ＞link;
t1 = t1- ＞link;

else

(2)
p = prior - ＞ link;

t1 = t- ＞link;

if ( t1 ! : NULL) printf ("cannot find");
else

(3)
r = q- ＞link;
q- ＞link = p;
while (r ! = p)

u = r- ＞link;
(4)
q=r;
r = u;

(5)