NYOJ592spiral grid

#include <cstdio>
#include <cstring>
#include <cmath>

int s[110][100];
int v[110][100];
int t_cnt = 1;
bool flag ;
typedef struct node
{
int x,y;
int step;
} node;
node st,en,que[500000];
void init()

{
memset(s,0,sizeof(s));
int cnt = 10000;
//printf("!!");
for(int i = 0; i < 100; ++i)s[0][i] = cnt--;
for(int i = 1; i < 100; ++i)s[i][99] = cnt--;
for(int i = 98; i >= 0; --i)s[99][i] = cnt--;
for(int i = 98; i > 0; --i)s[i][0] = cnt--;
int i = 1,j = 1;
//printf("haha");
while(cnt > 0)
{
while(!s[i][j])s[i][j++] = cnt--;
--j;
++i;
while(!s[i][j])s[i++][j] = cnt--;
--i;
--j;
while(!s[i][j])s[i][j--] = cnt--;
++j;
--i;
while(!s[i][j])s[i--][j] = cnt--;
++i;
++j;
}

}
int isP[10000 + 5];

void prime()

{
memset(isP,-1,sizeof(isP));
isP[1] = 0;
for(int i = 2; i <= 10000; ++i)
{
if(isP[i])
{
for(int j = 2; j * i <= 10000; ++j)
{
isP[j * i] = 0;
}
}
}
}

int dx[] = {-1,0,1,0};
int dy[] = {0,1,0,-1};

void bfs()

{
memset(que,0,sizeof(que));
node t,temp;
st.step = 0;
int head,tail;
head = tail = 0;
que[tail++] = st;
while(head < tail)
{
temp = que[head++];
for(int i = 0;i < 4;++i)
{
t.x = temp.x + dx[i];
t.y = temp.y + dy[i];
t.step = temp.step + 1;
if(t.x == en.x && t.y == en.y)
{
flag = true;
printf("Case %d: %d\n",t_cnt++,t.step);
return ;
}
if(t.x >= 0&& t.x <100&&t.y>=0&&t.y<100&&!isP[s[t.x][t.y]]&&!v[t.x][t.y])
{
v[t.x][t.y] = 1;
que[tail++] = t;
}
}
}
}
int main()

{
int a,b;
init();
prime();

while(~scanf("%d%d",&a,&b))
{
if(isP[b])
printf("Case %d: impossible\n",t_cnt++);
else if(a == b)
printf("Case %d: 0\n",t_cnt++);
else
{
memset(v,0,sizeof(v));
flag = false;
for(int i = 0; i < 100; ++i)
for(int j = 0; j < 100; ++j)
if(s[i][j] == a)
{
st.x = i;
st.y = j;
}
else if(s[i][j] == b)
{
en.x = i;
en.y = j;
}
v[st.x][st.y] = 1;
bfs();
if(!flag)
printf("Case %d: impossible\n",t_cnt++);
}
}
return 0;
}