搜索专题（复习）

hdu1241

DFS

#include <bits/stdc++.h>

using namespace std;
const int MAXN=105;
//char m[MAXN][MAXN];

char ma[MAXN][MAXN];
int n,m;
void dfs(int x,int y)
{
    if(x<0||x>=n||y<0||y>=m||ma[x][y]=='*')
        return;
    if(ma[x][y]=='@')
        ma[x][y]='*';
    dfs(x+1,y);
    dfs(x-1,y);
    dfs(x-1,y-1);
    dfs(x+1,y+1);
    dfs(x-1,y+1);
    dfs(x+1,y-1);
    dfs(x,y+1);
    dfs(x,y-1);

}
int main()
{
    //cout << "Hello world!" << endl;


    while(cin>>n>>m)
    {
        if(n==0&&m==0)
            return 0;
        int cnt=0;

        for(int i=0;i<n;i++)
        {
            cin>>ma[i];
        }
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                if(ma[i][j]=='@')
                {
                    cnt++;
                    dfs(i,j);
                }
            }
        }
        cout<<cnt<<endl;
    }
    return 0;
}

---

BFS

#include <bits/stdc++.h>

using namespace std;
const int MAXN=105;
char ma[MAXN][MAXN];
int n,m;
int x[]={-1,-1,0,1,1,1,0,-1};
int y[]={0,1,1,1,0,-1,-1,-1};
struct Node
{
    int x,y;
}node;
int check(int x,int y)
{
    if(x<0||x>=n||y<0||y>=m||ma[x][y]=='*')
        return 0;
    return 1;
}

void bfs()
{
    queue<Node>que;
    que.push(node);
    Node now,next;
    while(!que.empty())
    {
        now=que.front();
        que.pop();
        for(int i=0;i<8;i++)
        {
            next.x=now.x+x[i];
            next.y=now.y+y[i];
            if(check(next.x,next.y))
            {
                ma[next.x][next.y]='*';
                que.push(next);
            }
        }

    }

}


int main()
{
    while(cin>>n>>m)
    {
        if(n==0&&m==0)
            return 0;
        int cnt=0;
        for(int i=0;i<n;i++)
            cin>>ma[i];
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                if(ma[i][j]=='@')
                {
                    cnt++;
                    node.x=i;
                    node.y=j;
                    bfs();
                }
            }
        }
        cout<<cnt<<endl;
    }
    return 0;
}

POJ 3278Catch That Cow

BFS采用结构体写的话怎么剪枝都超时，采用int型的话可以过，没弄懂哪里出了问题

AC代码：

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;

int visit[100005] = {0};
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m) != EOF)
    {
        memset(visit,0,sizeof(visit));
        queue<int> q;
        q.push(n);int t;
        while(!q.empty())
        {
            t = q.front();
            q.pop();
            if(t == m)
            {
                break;
            }
            if(t > 0 && !visit[t-1])
            {
                int z;z = t-1; visit[z] = visit[t]+1;
                q.push(z);
            }
            if(t < m &&!visit[t+1])
            {
                  int z;z = t+1; visit[z] = visit[t]+1;
                q.push(z);
            }
            if(t*2 < 100005 && !visit[t*2])
            {
                int z;z = t*2; visit[z] = visit[t]+1;
                q.push(z);
            }
        }
        printf("%d\n",visit[m]);
    }
    return 0;
}

卡了的代码：

#include <iostream>
#include<queue>
#include<algorithm>
#include<string.h>
#include<math.h>
#include<stdio.h>
using namespace std;

const int MAXN=200005;
bool vis[MAXN];
int n,k;
int st=MAXN;




struct Node
{
    int x;
    int step;
}node;

void bfs()
{
    queue<Node>que;
    que.push(node);
    vis[node.x]=1;
    Node now,next;
    node.step=0;
    while(!que.empty())
    {
        now=que.front();
        que.pop();
        if(now.x==k)
        {
            st=min(st,now.step);
            return;
        }
        if(now.x>0&&!vis[now.x-1])
        {
            next.x=now.x-1;next.step=now.step+1;que.push(next);

        }
        if(now.x<k&&!vis[now.x+1])
        {
            next.x=now.x+1;next.step=now.step+1;que.push(next);
        }

        if(now.x*2<=100005&&!vis[now.x*2])
        {
            next.x=now.x*2;next.step=now.step+1;que.push(next);
        }
    }

}
int main()
{
    cin>>n>>k;
    node.x=n;
    bfs();
    cout<<st<<endl;

    return 0;
}

HDU2612 Find a way

两次BFS，分别计算每个人到达每个KFC需要的最少时间

#include<bits/stdc++.h>
using namespace std;
const int MAXN=205;
const int INF=0x3f3f3f3f;
char ma[MAXN][MAXN];
int kfc[MAXN][MAXN];
int len[3][MAXN*MAXN];
bool vis[MAXN][MAXN];

int dirx[]={0,0,1,-1};
int diry[]={1,-1,0,0};

int n,m;

struct Node
{
    int x,y,step;
}node;

bool check(int x,int y)
{
    if(x<0||x>=n||y<0||y>=m||ma[x][y]=='#'||vis[x][y])
        return 0;
    return 1;
}

void bfs(int x,int y,int p)
{
    node.x=x,node.y=y;node.step=0;
    queue<Node>que;
    que.push(node);

    vis[node.x][node.y]=1;


    Node now,next;
    while(!que.empty())
    {
        now=que.front();
        que.pop();
       //cout<<now.x<<" "<<now.y<<endl;
        if(ma[now.x][now.y]=='@')
        {
            len[p][kfc[now.x][now.y]]=now.step;
            //return;
        }
        for(int i=0;i<4;i++)
        {
            next.x=now.x+dirx[i];
            next.y=now.y+diry[i];
            next.step=now.step+1;
            if(check(next.x,next.y))
            {
                que.push(next);
                vis[next.x][next.y]=1;
            }
        }


    }



}

int main()
{
    while(cin>>n>>m)
    {
        //memset(len,40005,sizeof(len));
        memset(vis,0,sizeof(vis));
        int yx,yy,mx,my;
        int cnt=0,ans=INF;
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                cin>>ma[i][j];
                if(ma[i][j]=='Y')yx=i,yy=j;
                if(ma[i][j]=='M')mx=i,my=j;
                if(ma[i][j]=='@')kfc[i][j]=cnt++;
            }
        }
        bfs(yx,yy,0);
        memset(vis,0,sizeof(vis));
        bfs(mx,my,1);
        for(int i=0;i<cnt;i++)
        {
            ans=min(ans,(len[0][i]+len[1][i]));
        }
        cout<<ans*11<<endl;
    }


}