BFS 与 DFS

一般有个结论，问（最少）多少秒到达用BFS，问能不能（在恰当时候）到达用DFS

HDU 1241 http://acm.hdu.edu.cn/showproblem.php?pid=1241

#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
int n,m;
char a[150][150];
int sum;
int dir[8][2]={{1,0},{-1,0},{0,1},{0,-1},{1,1},{-1,-1},{1,-1},{-1,1}};
void dfs(int i,int j)
{
    if(i>n||j>m||i<=0||j<=0)
    return;
    for(int k=0;k<8;k++)
    {
        if(a[i+dir[k][0]][j+dir[k][1]]=='@')
        {
            a[i+dir[k][0]][j+dir[k][1]]='*';
            dfs(i+dir[k][0],j+dir[k][1]);

        }
    }
}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        memset(a,0,sizeof(a));
        getchar();
        sum=0;
        if(n==0&&m==0)
        break;
        int i,j;
        for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
        cin>>a[i][j];
        for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
        {
            if(a[i][j]=='@')
            {
                sum++;
                a[i][j]='*';
                dfs(i,j);
            }


        }
        printf("%d\n",sum);

    }
}

HDU 1242 http://acm.hdu.edu.cn/showproblem.php?pid=1242

#include<stdio.h>

int N,M;
char map[200][200];
char c;
int ai,aj,ri,rj;
int mintime[200][200];
int move[4][2]={{-1,0},{1,0},{0,-1},{0,1}};

int inarea(int x,int y)
{
    return x>0 && y>0 && x<=N && y<=M && map[x][y]!='#';
}

void dfs(int x,int y,int time)
{
    mintime[x][y]=time;
    for(int i=0; i<4; i++)
    {
        if(inarea(x+move[i][0],y+move[i][1]) && time+1+(map[x+move[i][0]][y+move[i][1]]=='x'?1:0)<mintime[x+move[i][0]][y+move[i][1]])
        {
            dfs(x+move[i][0],y+move[i][1],time+1+(map[x+move[i][0]][y+move[i][1]]=='x'? 1:0));
        }
    }
}

int main()
{

    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    while(scanf("%d%d",&N,&M)!=EOF)
    {
        for (int i=1; i<=N; i++) {
            for (int j=1; j<=M; j++) {
                mintime[i][j]=100000000;
            }
        }

    for (int i=1; i<=N; i++) {
            for (int j=1; j<=M; j++) {
                c=getchar();
                if (c=='a') {
                    ai=i;
                    aj=j;
                    map[i][j]='.';
                }
                else if (c=='r') {
                    ri=i;
                    rj=j;
                    map[i][j]='.';
                }
                else {
                    map[i][j]=c;
                }

            }
            getchar();
        }
        dfs(ri,rj,0);

        if(mintime[ai][aj]==100000000) printf("Poor ANGEL has to stay in the prison all his life.\n");
        else printf("%d\n",mintime[ai][aj]);

    }
    //fclose(stdin);
    //fclose(stdout);
    return 0;

}

 HDU 1312 http://acm.hdu.edu.cn/showproblem.php?pid=1312

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<queue>
using namespace std;
int n,m;
char a[50][50];
int si,sj;
int sum;
int move[4][2]={{1,0},{-1,0},{0,1},{0,-1}};

struct node
{
    int x;
    int y;
}w,ww;

void bfs()
{
    queue<node>q;
    w.x=si;
    w.y=sj;
    q.push(w);
    while(!q.empty())
    {
        ww=q.front();
        q.pop();
        for(int k=0;k<4;k++)
        {
            w=ww;
            w.x+=move[k][0];
            w.y+=move[k][1];
            if(a[w.x][w.y]=='.'&&w.x>0&&w.y>0&&w.x<=m&&w.y<=n)
            {
                sum++;
                a[w.x][w.y]='#';
                q.push(w);
            }
        }
    }
}

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        if(n==0&&m==0)
        break;
        int i,j;
        for(i=1;i<=m;i++)
            for(j=1;j<=n;j++)
            {
                cin>>a[i][j];
                if(a[i][j]=='@')
                {
                    si=i;
                    sj=j;
                }
            }

        sum=0;
        bfs();
        printf("%d\n",sum+1);
    }
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}

 HDU 2717 http://acm.hdu.edu.cn/showproblem.php?pid=2717

#include<stdio.h>
#include<string.h>
#include<queue>
using namespace std;
int n,m;
int vis[2500000];
int ans;

struct node
{
    int x;int step;
}w,p,q;
queue<node>Q;

void bfs()
{
    Q.push(w);
    while(!Q.empty())
    {
        p=Q.front();
        Q.pop();
        if(p.x==m)
        {
            ans=p.step;
            return;
        }
        p.step++;
        if(!vis[p.x]&&p.x>0)
        {
            q=p;
            q.x--;
            Q.push(q);
        }
        if(!vis[p.x]&&p.x<m)
        {
            q=p;
            q.x*=2;
            Q.push(q);
        }
        if(!vis[p.x])
        {
            q=p;
            q.x++;
            vis[p.x]=1;
            Q.push(q);
        }
    }

}

int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        memset(vis,0,sizeof(vis));
        ans=0;
        w.x=n;
        w.step=0;
        bfs();
        printf("%d\n",ans);
        while(!Q.empty())
        Q.pop();

    }
    return 0;
}

 HDU 1372 http://acm.hdu.edu.cn/showproblem.php?pid=1372

#include<stdio.h>
#include<string.h>
#include<iostream>
#include<queue>
using namespace std;
int dir[8][2]={{2,1},{2,-1},{-2,-1},{-2,1},{1,2},{1,-2},{-1,2},{-1,-2}};
int map[10][10];
char n[3],m[3];
int ai,aj,bi,bj;
int ans;

struct node
{
    int x;
    int y;
    int step;
}w,p,q;
queue<node>Q;
void bfs()
{
    while(!Q.empty())
    {
        p=Q.front();
        Q.pop();
        if(p.x<=0||p.y<=0||p.x>8||p.y>8||map[p.y][p.x])
        continue;
        if(p.x==bj&&p.y==bi)
        {
            ans=p.step;
            return;
        }
        p.step++;
        map[p.y][p.x]++;
        for(int k=0;k<8;k++)
        {
            q=p;
            q.x+=dir[k][0];
            q.y+=dir[k][1];
            Q.push(q);

        }
    }
}

int main()
{
    while(scanf("%s%s",&n,&m)!=EOF)
    {
        aj=n[0]-'a'+1;
        ai=n[1]-'0';
        bj=m[0]-'a'+1;
        bi=m[1]-'0';
        ans=0;
        w.x=aj;
        w.y=ai;
        w.step=0;
        memset(map,0,sizeof(map));
        Q.push(w);
        bfs();
        printf("To get from %s to %s takes %d knight moves.\n",n,m,ans);
        while(!Q.empty())
        Q.pop();
    }
    return 0;
}