5.1 基础题目选讲

  1 #include<cstdio>
  2 #include<cstring>
  3 #include<queue>
  4 #define mt(a,b) memset(a,b,sizeof(a))
  5 using namespace std;
  6 const int inf=0x3f3f3f3f;
  7 const int M=1024;
  8 int t,n,m;
  9 char a[M][M];
 10 int d[M][M];
 11 int dx[]={0,0,1,-1};
 12 int dy[]={1,-1,0,0};
 13 struct Q{
 14     int x,y,step;
 15 }now,pre;
 16 queue<Q> q;
 17 bool inside(const int &x,const int &y){
 18     if(x>=0&&x<n&&y>=0&&y<m) return true; return false;
 19 }
 20 void bfs(){
 21     for(int i=0;i<n;i++){
 22         for(int j=0;j<m;j++){
 23             d[i][j]=inf;
 24         }
 25     }
 26     while(!q.empty()) q.pop();
 27     for(int i=0;i<n;i++){
 28         for(int j=0;j<m;j++){
 29             if(a[i][j]==‘F‘){
 30                 now.x=i;
 31                 now.y=j;
 32                 now.step=0;
 33                 d[i][j]=0;
 34                 q.push(now);
 35             }
 36         }
 37     }
 38     while(!q.empty()){
 39         pre=q.front();
 40         q.pop();
 41         for(int i=0;i<4;i++){
 42             int tx=pre.x+dx[i];
 43             int ty=pre.y+dy[i];
 44             if(!inside(tx,ty)||a[tx][ty]==‘#‘) continue;
 45             now.step=pre.step+1;
 46             if(d[tx][ty]>now.step){
 47                 d[tx][ty]=now.step;
 48                 now.x=tx;
 49                 now.y=ty;
 50                 q.push(now);
 51             }
 52         }
 53     }
 54 }
 55 bool out(const Q &a){
 56     if(a.x==0||a.x==n-1||a.y==0||a.y==m-1) return true; return false;
 57 }
 58 bool vis[M][M];
 59 int solve(){
 60     mt(vis,0);
 61     while(!q.empty()) q.pop();
 62     for(int i=0;i<n;i++){
 63         for(int j=0;j<m;j++){
 64             if(a[i][j]==‘J‘){
 65                 vis[i][j]=true;
 66                 now.x=i;
 67                 now.y=j;
 68                 now.step=0;
 69                 q.push(now);
 70             }
 71         }
 72     }
 73     while(!q.empty()){
 74         pre=q.front();
 75         q.pop();
 76         if(out(pre)) return pre.step+1;
 77         for(int i=0;i<4;i++){
 78             int tx=pre.x+dx[i];
 79             int ty=pre.y+dy[i];
 80             if(!inside(tx,ty)||a[tx][ty]==‘#‘||vis[tx][ty]||d[tx][ty]<=pre.step+1) continue;
 81             vis[tx][ty]=true;
 82             now.x=tx;
 83             now.y=ty;
 84             now.step=pre.step+1;
 85             q.push(now);
 86         }
 87     }
 88     return -1;
 89 }
 90 int main(){
 91     while(~scanf("%d",&t)){
 92         while(t--){
 93             scanf("%d%d",&n,&m);
 94             for(int i=0;i<n;i++){
 95                 scanf("%s",a[i]);
 96             }
 97             bfs();
 98             int ans=solve();
 99             if(~ans) printf("%d\n",ans);
100             else puts("IMPOSSIBLE");
101         }
102     }
103     return 0;
104 }

  1 #include<cstdio>
  2 #include<algorithm>
  3 #include<queue>
  4 using namespace std;
  5 const int inf=0x3f3f3f3f;
  6 const int M=32;
  7 int n,m;
  8 char a[M][M];
  9 int dp[M][M][8][4];
 10 struct Q{
 11     int x,y,step,color,dir;
 12 }now,pre;
 13 queue<Q> q;
 14 int dx[]={-1,0,1,0};
 15 int dy[]={0,1,0,-1};
 16 Q turnright(const Q &pre){
 17     Q now;
 18     now.color=pre.color;
 19     now.x=pre.x;
 20     now.y=pre.y;
 21     now.dir=(pre.dir+1)%4;
 22     now.step=pre.step+1;
 23     return now;
 24 }
 25 Q turnleft(const Q &pre){
 26     Q now;
 27     now.color=pre.color;
 28     now.x=pre.x;
 29     now.y=pre.y;
 30     now.dir=pre.dir-1;
 31     if(now.dir==-1) now.dir=3;
 32     now.step=pre.step+1;
 33     return now;
 34 }
 35 Q ahead(const Q &pre){
 36     Q now;
 37     now.color=(pre.color+1)%5;
 38     now.x=pre.x+dx[pre.dir];
 39     now.y=pre.y+dy[pre.dir];
 40     now.dir=pre.dir;
 41     now.step=pre.step+1;
 42     return now;
 43 }
 44 bool inside(const Q &now){
 45     if(now.x>=0&&now.x<n&&now.y>=0&&now.y<m) return true; return false;
 46 }
 47 void go(const Q &now){
 48     if(!inside(now)||a[now.x][now.y]==‘#‘) return ;
 49     if(dp[now.x][now.y][now.color][now.dir]>now.step){
 50         dp[now.x][now.y][now.color][now.dir]=now.step;
 51         q.push(now);
 52     }
 53 }
 54 void bfs(){
 55     for(int i=0;i<n;i++){
 56         for(int j=0;j<m;j++){
 57             for(int k=0;k<5;k++){
 58                 for(int u=0;u<4;u++){
 59                     dp[i][j][k][u]=inf;
 60                 }
 61             }
 62         }
 63     }
 64     for(int i=0;i<n;i++){
 65         for(int j=0;j<m;j++){
 66             if(a[i][j]==‘S‘){
 67                 now.x=i;
 68                 now.y=j;
 69             }
 70         }
 71     }
 72     dp[now.x][now.y][0][0]=0;
 73     now.color=0;
 74     now.dir=0;
 75     now.step=0;
 76     while(!q.empty()) q.pop();
 77     q.push(now);
 78     while(!q.empty()){
 79         pre=q.front();
 80         q.pop();
 81         now=turnright(pre);
 82         go(now);
 83         now=turnleft(pre);
 84         go(now);
 85         now=ahead(pre);
 86         go(now);
 87     }
 88 }
 89 int main(){
 90     int cas=1;
 91     while(~scanf("%d%d",&n,&m),n|m){
 92         for(int i=0;i<n;i++){
 93             scanf("%s",a[i]);
 94         }
 95         bfs();
 96         int ex,ey;
 97         for(int i=0;i<n;i++){
 98             for(int j=0;j<m;j++){
 99                 if(a[i][j]==‘T‘){
100                     ex=i;
101                     ey=j;
102                 }
103             }
104         }
105         if(cas>1) puts("");
106         printf("Case #%d\n",cas++);
107         int ans=inf;
108         for(int i=0;i<4;i++){
109             ans=min(ans,dp[ex][ey][0][i]);
110         }
111         if(ans<inf){
112             printf("minimum time = %d sec\n",ans);
113         }
114         else{
115             puts("destination not reachable");
116         }
117     }
118     return 0;
119 }