UVa 10422 - Knights in FEN

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>

using namespace std;
const int MAXSIZE = 600005;
char knight[26] = "111110111100 110000100000";
char a[5][5], save[MAXSIZE][26];
int head[MAXSIZE], next[MAXSIZE], num, f_val;
int step_x[8] = {-2,2,2,-2,1,1,-1,-1};
int step_y[8] = {-1,-1,1,1,2,-2,2,-2};
int Hash()
{
int sum = 0, seed = 131, i;
for(i=0; i<25; i++)
sum = sum * seed + save[num][i];
return (sum & 0x7FFFFFFF) % 600003;
}
bool nextval()
{
int h = Hash();
int u = head[h];
while(u)
{
if(!strcmp(save[num], save[u]))
return false;
u = next[u];
}
next[num] = head[h];
head[h] = num;
return true;
}
void Copy(int s) // 将二维数组转换为一维数组
{
int tot = 0, i, j;
for(i=0; i<5; i++)
for(j=0; j<5; j++)
save[s][tot++] = a[i][j];
}
void char_swap(int x1, int y1, int x2, int y2) // 交换两个位置的元素
{
char c = a[x1][y1];
a[x1][y1] = a[x2][y2];
a[x2][y2] = c;
}
void dfs(int cur,int x, int y)
{
if(cur>=10)
return ;
int flag = 0;
for(int i=0; i<8; i++)
{
int xx = x+step_x[i];
int yy = y+step_y[i];
if(xx>=0 && xx<5 && yy>=0 && yy<5)
{
char_swap(xx, yy, x, y);
Copy(num);
if(!strcmp(save[num],knight))
{
if(f_val>cur)
f_val = cur;
char_swap(xx, yy, x, y);
return ;
}
if(nextval()) // 剪枝，如果与前面的棋谱相通则不必再搜下去
{
++num;
dfs(cur+1, xx, yy);
--num;
}
char_swap(xx, yy, x, y);
}
}
}
int main()
{
#ifdef test
freopen("sample.txt", "r", stdin);
#endif
int t,x,y;
scanf("%d", &t);
while(t--)
{
num = 1;
f_val = 20;
memset(head, 0, sizeof(head));
for(int i=0; i<5; i++)
{
getchar();
for(int j=0; j<5; j++)
{
scanf("%c", &a[i][j]);
if(a[i][j] == ' ')
{
x = i;
y = j;
}
}
}
Copy(num);
if(!strcmp(save[num],knight)) // 判断最开始的图是不是直接符合要求
f_val = -1;
else
dfs(0, x, y);
++num;
if(f_val < 20)
printf("Solvable in %d move(s).\n", f_val+1);
else
printf("Unsolvable in less than 11 move(s).\n");
}
return 0;
}