poj - 2255 Tree Recovery

#include <stdio.h>
#include <string.h>
int cnt;
char c[30];
void build(char * s,char * t,int l)
{
if(l == 1)
{c[cnt++] = *s; return ;}
int n = strchr(t,s[0]) - t;
if(n) build(s+1,t,n);
if(l-n-1)
build(s+n+1,t+n+1,l-n-1);
c[cnt++] = *s;
}
int main()
{
char a[30],b[30];
int l,i;
while(~scanf("%s%s",a,b))
{
cnt = 0;
l = strlen(a);
build(a,b,l);
for(i = 0; i < l; i++)
printf("%c",c[i]);
printf("\n");
}
return 0;
}