poj 1154

来源：互联网发布：飞鸽传书网络打印机编辑：程序博客网时间：2024/06/05 18:25

第一阶段未懂回溯#include <iostream>#include <fstream>#include <cstring>using namespace std;const int MAXN=30;char maze[MAXN][MAXN];int vis[MAXN][MAXN];int counter=0;int letter[26];void DFS(int x,int y){    if(vis[x][y] || maze[x][y]=='#' || letter[maze[x][y]-65]==1)return ;    vis[x][y]=1;    counter++;    letter[maze[x][y]-65]=1;    DFS(x-1,y);    DFS(x,y-1);    DFS(x+1,y);    DFS(x,y+1);}int main(){    //cout << "Hello world!" << endl;    //freopen("input.txt","r",stdin);    int R,C;    while(cin>>R>>C)        {    memset(vis,0,sizeof(vis));    memset(maze,'#',sizeof(maze));    memset(letter,0,sizeof(letter));    for(int i=1;i<=R;i++)    {        for(int j=1;j<=C;j++)        {            cin>>maze[i][j];        }    }    DFS(1,1);    cout<<counter<<endl;    //output maze    /*    for(int i=0;i<=R+1;i++)    {        for(int j=0;j<=C+1;j++)        {            cout<<maze[i][j];        }        cout<<endl;    }*/    //fclose(stdin);    }    return 0;}

第二阶段应用回溯

#include <iostream>#include <fstream>#include <cstring>#include <cstdio>using namespace std;const int MAXN=30;char map[MAXN][MAXN];int vis[MAXN][MAXN];int letter[26];int sum=1;int total=0;int Dir_x[4]={0,1,0,-1};int Dir_y[4]={-1,0,1,0};int R,C;void DFS(int x,int y){    vis[x][y]=1;    int nextx,nexty;    if(sum>total)total=sum;    for(int i=0;i<4;i++)    {        nextx=x+Dir_x[i];        nexty=y+Dir_y[i];        if(nextx>=0 && nextx<R && nexty>=0 && nexty<C && !letter[map[nextx][nexty]-'A']            && !vis[nextx][nexty])        {            letter[map[x][y]-'A']=1;            sum++;            DFS(nextx,nexty);            sum--;            letter[map[x][y]-'A']=0;            vis[x][y]=0;        }    }}int main(){    //cout << "Hello world!" << endl;    //freopen("input.txt","r",stdin);    //while(scanf("%d %d",&R,&C)==2)    cin>>R>>C;    {        //if(R==0 || C==0)break;        memset(letter,0,sizeof(letter));        memset(vis,0,sizeof(vis));        //memset()        for(int i=0;i<R;i++)        {            for(int j=0;j<C;j++)            {                cin>>map[i][j];            }        }        DFS(0,0);        cout<<total<<endl;    }    //fclose(stdin);    return 0;}

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