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1103Hike on a Graph.cpp
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132 lines (125 loc) · 2.28 KB
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/*
ZJU 1103 Hike on a Graph
00:00.09 4348
2004.07.14 by adai
*/
#include <iostream>
using namespace std;
class state{
public:
int x;
int y;
int z;
int visited;
state &operator=(const state &c){
x=c.x;
y=c.y;
z=c.z;
visited=c.visited;
return *this;
}
}a[50][50][50];
state queue[50*50*50];
int n;
char color[50][50];
int head,tail;
int nhead,ntail;
int depth;
void order(int &p1,int &p2,int &p3)
{
int m;
if (p1>p2)
{
m=p1,p1=p2,p2=m;
}
if (p1>p3)
{
m=p1,p1=p3,p3=m;
}
if (p2>p3)
{
m=p2,p2=p3,p3=m;
}
}
int bfs(void){
int i,j;
while(tail-head>=0){
for(i=head;i<=tail;i++){
if(queue[i].x==queue[i].y&&queue[i].y==queue[i].z){
return depth;
}
}
depth++;
nhead=tail+1;
ntail=tail;
int s1,s2,s3;
for(i=head;i<=tail;i++){
for(j=0;j<n;j++){
if(j==queue[i].x) continue;
if(color[j][queue[i].x]!=color[queue[i].y][queue[i].z]) continue;
s1=j,s2=queue[i].y,s3=queue[i].z;
order(s1,s2,s3);
if(a[s1][s2][s3].visited==1) continue;
a[s1][s2][s3].visited=1;
queue[++ntail]=a[s1][s2][s3];
}
for(j=0;j<n;j++){
if(j==queue[i].y) continue;
if(color[j][queue[i].y]!=color[queue[i].x][queue[i].z]) continue;
s1=queue[i].x,s2=j,s3=queue[i].z;
order(s1,s2,s3);
if(a[s1][s2][s3].visited==1) continue;
a[s1][s2][s3].visited=1;
queue[++ntail]=a[s1][s2][s3];
}
for(j=0;j<n;j++){
if(j==queue[i].z) continue;
if(color[j][queue[i].z]!=color[queue[i].x][queue[i].y]) continue;
s1=queue[i].x,s2=queue[i].y,s3=j;
order(s1,s2,s3);
if(a[s1][s2][s3].visited==1) continue;
a[s1][s2][s3].visited=1;
queue[++ntail]=a[s1][s2][s3];
}
}
for(i=nhead;i<=ntail;i++){
queue[i-nhead]=queue[i];
}
head=0;
tail=ntail-nhead;
}
return -1;
}
int main(){
int min;
int p1,p2,p3;
int i,j,t;
while(1){
cin>>n;
if(n==0) break;
cin>>p1>>p2>>p3;
p1--,p2--,p3--;
for(i=0;i<n;i++){
for(j=0;j<n;j++) cin>>color[i][j];
}
for(i=0;i<n;i++){
for(j=0;j<n;j++){
for(t=0;t<n;t++){
a[i][j][t].x=i;
a[i][j][t].y=j;
a[i][j][t].z=t;
a[i][j][t].visited=0;
}
}
}
order(p1,p2,p3);
a[p1][p2][p3].visited=1;
queue[0]=a[p1][p2][p3];
head=tail=0;
depth=0;
min=bfs();
if(min==-1) cout<<"impossible"<<endl;
else cout<<min<<endl;
}
return 0;
}