POJ 3170（Knights of Ni）（BFS）

#include<cstdio>
#include<queue>
#include<cstring>
#include<iostream>
#include<algorithm>
#define debu
using namespace std;
const int dx[]= {-1,1,0,0};
const int dy[]= {0,0,-1,1};
const int  INF=0x3f3f3f3f;
const int maxn=1000+50;
struct Node
{
int x,y;
Node(int x=0,int y=0):x(x),y(y) {}
};
queue<Node> q;
vector<Node> shr;
int n,m,stx,sty,edx,edy;
int dist[2][maxn][maxn];
int g[maxn][maxn],v[maxn][maxn];
void solve(int id,int x,int y)
{
memset(v,0,sizeof(v));
while(!q.empty()) q.pop();
memset(dist[id],INF,sizeof(dist[id]));
v[x][y]=1,q.push(Node(x,y)),dist[id][x][y]=0;
while(!q.empty())
{
Node now=q.front();
q.pop();
for(int i=0; i<4; i++)
{
int x=now.x+dx[i];
int y=now.y+dy[i];
if(x>=1&&x<=n&&y>=1&&y<=m&&(g[x][y]!=1)&&(!v[x][y]))
{
dist[id][x][y]=dist[id][now.x][now.y]+1;
v[x][y]=1,q.push(Node(x,y));
}
}
}
}
int main()
{
#ifdef debug
freopen("in.txt","r",stdin);
#endif // debug
scanf("%d%d",&m,&n);
for(int i=1; i<=n; i++)
for(int j=1; j<=m; j++)
{
scanf("%d",&g[i][j]);
if(g[i][j]==4) shr.push_back(Node(i,j));
if(g[i][j]==2) stx=i,sty=j;
if(g[i][j]==3) edx=i,edy=j;
}
solve(0,stx,sty);
solve(1,edx,edy);
int ans=INF;
for(int i=0; i<shr.size(); i++)
{
int x=shr[i].x;
int y=shr[i].y;
ans=min(ans,dist[0][x][y]+dist[1][x][y]);
}
printf("%d\n",ans);
return 0;
}