迭代加深搜索。
剪枝：当满足以下任意一个条件退出：
1.当前已搜到答案时（ans!=-1||sum==0）
2.剩余步数+1<当前局面与目标局面不同的格子数sum 时（因为n步最多改变n+1个格子）
3.当前步数>当前规定最大步数时
1 #include<cstdio> 2 #include<cstring> 3 using namespace std; 4 const int n=5,m=8,maxstep=15; 5 int a[6][6],b[6][6]={{0,0,0,0,0,0}, 6 {0,1,1,1,1,1},{0,0,1,1,1,1}, 7 {0,0,0,-1,1,1},{0,0,0,0,0,1}, 8 {0,0,0,0,0,0}}; 9 int fh[9]={0,-2,-1,1,2,2,1,-1,-2}, 10 fl[9]={0,1,2,2,1,-1,-2,-2,-1}; 11 int ex,ey,ans,step; 12 void swap(int,int,int,int),work(), 13 dfs(int,int,int),read(); 14 int change(char),check(),pd(int,int); 15 int main(){ 16 int t; 17 scanf("%d",&t); 18 for (int i=1;i<=t;i++) work(); 19 return 0; 20 } 21 void work(){ 22 ans=-1;read(); 23 for (step=0;step<=maxstep;step++){ 24 dfs(0,ex,ey); 25 if (ans!=-1) break; 26 } 27 printf("%d\n",ans); 28 return; 29 } 30 void read(){ 31 char c[7]; 32 for (int i=1;i<=n;i++){ 33 scanf("%s",&c); 34 for (int j=0;j<n;j++){ 35 a[i][j+1]=change(c[j]); 36 if (a[i][j+1]==-1){ 37 ex=i;ey=j+1; 38 } 39 } 40 } 41 return; 42 } 43 void dfs(int deep,int p,int q){ 44 int x,y,sum; 45 if (ans!=-1) return; 46 sum=check(); 47 if (deep==step){ 48 if (!sum) ans=deep;return; 49 } 50 else if (step-deep+1<sum) return; 51 if (deep>step) return; 52 for (int i=1;i<=m;i++){ 53 x=p+fh[i];y=q+fl[i]; 54 if (pd(x,y)){ 55 swap(x,y,p,q); 56 dfs(deep+1,x,y); 57 swap(x,y,p,q); 58 } 59 } 60 } 61 int change(char c){ 62 if (c=='1') return 1; 63 if (c=='0') return 0; 64 if (c=='*') return -1; 65 } 66 int check(){ 67 int sum=0; 68 for (int i=1;i<=n;i++) 69 for (int j=1;j<=n;j++) 70 if (a[i][j]!=b[i][j]) sum++; 71 return sum; 72 } 73 int pd(int p,int q){ 74 if (p>=1&&q>=1&&p<=n&&q<=n) return 1; 75 return 0; 76 } 77 void swap(int x,int y,int p,int q){ 78 int tmp; 79 tmp=a[x][y];a[x][y]=a[p][q];a[p][q]=tmp; 80 return; 81 }
