UVA 1515 (最小割)

来源：互联网发布：更新mac系统版本出错编辑：程序博客网时间：2024/05/22 03:23
额...感觉关键还是要看出是最小割,然后用割的思想去考虑怎么建图...
然后慢一点的最大流方法会被卡掉
#include <iostream>#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>#include <vector>#include <queue>using namespace std;const int INF = 1e8;#define maxn 3333#define maxm 411111int n, m;int s, t;int dd, ff, bb;struct Edge{    int from, to,next,cap,flow;    void get(int u,int a,int b,int c,int d)    {        from = u; to = a; next = b; cap = c; flow = d;    }}edge[maxm];int tol;int head[maxn];int gap[maxn],dep[maxn],pre[maxn],cur[maxn];void init(){    tol=0;    memset(head,-1,sizeof(head));}void add_edge(int u,int v,int w,int rw=0){    edge[tol].get(u, v,head[u],w,0);head[u]=tol++;    edge[tol].get(v, u,head[v],rw,0);head[v]=tol++;}int sap(int start,int end,int N){    memset(gap,0,sizeof(gap));    memset(dep,0,sizeof(dep));    memcpy(cur,head,sizeof(head));    int u=start;    pre[u]=-1;    gap[0]=N;    int ans=0;    while(dep[start]<N)    {        if(u==end)        {            int Min=INF;            for(int i=pre[u];i!=-1;i=pre[edge[i^1].to])                if(Min>edge[i].cap-edge[i].flow)                   Min=edge[i].cap-edge[i].flow;            for(int i=pre[u];i!=-1;i=pre[edge[i^1].to])            {                edge[i].flow+=Min;                edge[i^1].flow-=Min;            }            u = start;            ans+=Min;            continue;        }        bool flag=false;        int v;        for(int i=cur[u];i !=-1;i=edge[i].next)        {            v=edge[i].to;            if(edge[i].cap-edge[i].flow&&dep[v]+1==dep[u])            {                flag=true;                cur[u]=pre[v]=i;                break;            }        }        if(flag)        {            u=v;            continue;        }        int Min=N;        for(int i=head[u];i!=-1;i=edge[i].next)            if(edge[i].cap-edge[i].flow&&dep[edge[i].to]<Min)        {            Min=dep[edge[i].to];            cur[u]=i;        }        gap[dep[u]]--;        if(!gap[dep[u]]) return ans;        dep[u]=Min+1;        gap[dep[u]]++;        if(u!=start) u=edge[pre[u]^1].to;    }    return ans;}char mp[55][55];#define move  Moveconst int move[2][2] = {{0, 1}, {1, 0}};bool legal (int x, int y) {    if (x < 0 || x >= n || y < 0 || y >= m)        return 0;    return 1;}int main () {    //freopen ("in.txt", "r", stdin);    int tt;    scanf ("%d", &tt);    while (tt--) {        init ();        scanf ("%d%d", &m, &n);        scanf ("%d%d%d", &dd, &ff, &bb);        for (int i = 0; i < n; i++) {            scanf ("%s", mp[i]);        }        int add = 0;        for (int i = 0; i < m; i++) {            if (mp[0][i] == '.') {                add += ff;                mp[0][i] = '#';            }            if (mp[n-1][i] == '.') {                add += ff;                mp[n-1][i] = '#';            }        }        for (int i = 0; i < n; i++) {            if (mp[i][0] == '.') {                add += ff;                mp[i][0] = '#';            }            if (mp[i][m-1] == '.') {                add += ff;                mp[i][m-1] = '#';            }        }        int N = n*m+2, s = n*m, t = n*m+1;        for (int i = 0; i < n; i++) {//两点之间连边            for (int j = 0; j < m; j++) {                for (int k = 0; k < 2; k++) {                    int xx = i+move[k][0], yy = j+move[k][1];                    if (!legal (xx, yy))                        continue;                    add_edge (i*m+j, xx*m+yy, bb);                    add_edge (xx*m+yy, i*m+j, bb);                }            }        } //cout << ".." << endl;        for (int i = 0; i < n; i++) {            for (int j = 0; j < m; j++) {                if (i == 0 || i == n-1 || j == 0 || j == m-1) { //cout << i << "\\\\" << j << endl;                    add_edge (s, i*m+j, INF);                }                else {                    if (mp[i][j] == '.') {                        add_edge (i*m+j, t, ff);                    }                    else                        add_edge (s, i*m+j, dd);                }            }        }        //cout << add << endl;        int ans = sap (s, t, N);        printf ("%d\n", ans+add);    }    return 0;}
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