Hdu5093 [maximum stream]

Build a turret on *, and the turret will launch shells in four directions, like upper and lower. O is ice float, and shells will cross. # If it is an iceberg, shells will be blocked. The turret will attack each other and ask the maximum number of Turret not attacked each other.

I thought it was greedy, like a http://acm.hdu.edu.cn/showproblem.php? The PID = 1045 is the same. The result is wa. If you do not know whether it is wrong or invalid.

Later changed to http://acm.hdu.edu.cn/showproblem.php? The Network Flow Method with PID = 1045 is AC.

Create a graph: first use # to enclose the whole map and divide all vertices into two vertices: AB. The Source Vertex creates an edge to A and B to the sink vertex. For all * on the map, find the first # on the left side of the map and set it to A. The first # On the top is set to B. The a point of a creates an edge at B. The edge capacity is 1.

#include<iostream>#include<cstdio>#include<queue>using namespace std;const int NO=57;const int INF=1000000000;struct X{    int x,y;    X(){x=y=0;}    X(int a,int b){x=a;y=b;}}map[NO][NO],u[NO*NO*4],v[NO*NO*4],st,ed,r[NO][NO],c[NO][NO];char MAP[NO][NO];int n,m;int first[NO*2][NO*2],next[NO*NO*4],w[NO*NO*4],num;int dis[NO*2][NO*2];int ans[NO][NO];void reset_first(){    int i,j;    num=0;    for(i=0;i<=ed.x;i++)        for(j=0;j<=ed.y;j++)            first[i][j]=-1;}void add(int x1,int y1,int x2,int y2,int c){    u[num].x=x1,u[num].y=y1;    v[num].x=x2,v[num].y=y2;    w[num]=c;    next[num]=first[x1][y1];    first[x1][y1]=num++;    u[num].x=x2,u[num].y=y2;    v[num].x=x1,v[num].y=y1;    w[num]=0;    next[num]=first[x2][y2];    first[x2][y2]=num++;}void reset_dis(){    int i,j;    for(i=0;i<=ed.x;i++)        for(j=0;j<=ed.y;j++)            dis[i][j]=-1;}bool bfs(){    int i;    X a;    reset_dis();    queue<X> t;    t.push(st);    dis[st.x][st.y]=0;    while(!t.empty())    {        a=t.front();        t.pop();        for(i=first[a.x][a.y];i!=-1;i=next[i])            if(w[i]&&dis[v[i].x][v[i].y]==-1)            {                dis[v[i].x][v[i].y]=dis[a.x][a.y]+1;                t.push(v[i]);            }    }    return dis[ed.x][ed.y]!=-1;}int min(int a,int b){return a<b?a:b;}int dfs(const X &k,int MIN){    if(k.x==ed.x&&k.y==ed.y)        return MIN;    int sum=0,a,i;    for(i=first[k.x][k.y];i!=-1&&sum<MIN;i=next[i])        if(w[i]&&dis[v[i].x][v[i].y]==dis[k.x][k.y]+1&&(a=dfs(v[i],min(MIN-sum,w[i]))))        {            w[i]-=a;            w[i^1]+=a;            sum+=a;        }    if(!sum)        dis[k.x][k.y]=-1;    return sum;}int DANIC(){    int ans=0,a;    while(bfs())        while(a=dfs(st,INF))            ans+=a;    return ans;}void read(){    for(int i=0;i<=n+1;i++)        MAP[i][0]=MAP[i][m+1]=‘#‘;    for(int j=0;j<=m+1;j++)        MAP[0][j]=MAP[n+1][j]=‘#‘;    for(int i=1;i<=n;i++)    {        getchar();        for(int j=1;j<=m;j++)            MAP[i][j]=getchar();    }    for(int i=0;i<=n+1;i++)        for(int j=0;j<=m+1;j++)            if(MAP[i][j]==‘#‘)            {                ans[i][j]=-1;                map[i][j].x=MAP[i+1][j]!=‘#‘;                map[i][j].y=MAP[i][j+1]!=‘#‘;            }            else                ans[i][j]=map[i][j].x=map[i][j].y=0;}void build(){    int i,j,k;    for(i=0;i<=n;i++)        for(j=0;j<=m;j++)        {            if(map[i][j].x)            {                for(k=0;i+k+1<=n;k++)                    if(ans[i+k+1][j]==-1)                        break;                    else                        c[i+k+1][j].x=i,c[i+k+1][j].y=j;                add(n+i,m+j,ed.x,ed.y,1);            }            if(map[i][j].y)            {                for(k=0;j+k+1<=m;k++)                    if(ans[i][j+k+1]==-1)                        break;                    else                        r[i][j+k+1].x=i,r[i][j+k+1].y=j;                add(st.x,st.y,i,j,1);            }        }    for(i=1;i<=n;i++)        for(j=1;j<=m;j++)            if(MAP[i][j]==‘*‘)                add(r[i][j].x,r[i][j].y,n+c[i][j].x,m+c[i][j].y,1);}int main(){    int ttt;    scanf("%d",&ttt);    while(ttt--)    {        scanf("%d%d",&n,&m);        ed.x=n*2+1;ed.y=m*2+1;        reset_first();        read();        build();        printf("%d\n",DANIC());    }    return 0;}

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Hdu5093 [maximum stream]