HDU 3549 Flow Problem 网络流 基础题

DINIC求网络流最大流

贴代码（AC，125MS）

#include<iostream>#include<queue>#include<cstdlib>#include<vector>#include<cstring>#include<cstdio>using namespace std;const int INF = 0x7f7f7f7f;const int MAXN = 20;const int MAXM = 1005;int n, m, s, t, cnt;int head[MAXN];bool vis[MAXN];int d[MAXN], cur[MAXN], que[MAXN];struct edge_{    int from, to, cap, flow, next;}edge[MAXM];void init(){    memset(head, -1, sizeof(head));    memset(edge, -1, sizeof(edge));    cnt = 0;}void add(int from, int to, int cap){    edge[cnt].from = from, edge[cnt].to = to;    edge[cnt].cap = cap, edge[cnt].next = head[from];    edge[cnt].flow = 0;    head[from] = cnt++;    edge[cnt].from = to, edge[cnt].to = from;    edge[cnt].cap = 0, edge[cnt].next = head[to];    edge[cnt].flow = 0;    head[to] = cnt++;}bool bfs(){    memset(vis, false, sizeof(vis));    memset(d, 0, sizeof(d));    d[s] = 0, vis[s] = 1, que[0] = s;    int tail = 0, front = 1;    while(tail < front){        int x = que[tail++];        for(int now = head[x]; ~now; now = edge[now].next){            edge_ &e = edge[now];            if(!vis[e.to] && e.cap > e.flow){                vis[e.to] = 1;                d[e.to] = d[x] + 1;                que[front++] = e.to;            }        }    }    return vis[t];}int dfs(int x, int a){    if(x == t || a == 0)        return a;    int flow = 0, f;    for(int &now = cur[x]; ~now; now = edge[now].next){        edge_ &e = edge[now];        if(d[x] + 1 == d[e.to] && (f = dfs(e.to, min(a, e.cap - e.flow))) > 0){            e.flow +=f;            edge[now ^ 1].flow -= f;            flow += f;            a -= f;            if(a == 0)                break;        }    }    return flow;}int maxFlow(int _s, int _t, int _n, int _m){    s = _s, t = _t;    n = _n, m = _m;    int flow = 0;    while(bfs()){        for(int i = 1; i <= n; i++)            cur[i] = head[i];        flow += dfs(s, INF);    }    return flow;}int main(){    int n, m, s, t, c, ca = 1, num;    scanf("%d", &num);    while(num--){        init();        scanf("%d%d", &n, &m);        for(int i = 0; i < m; i++){            scanf("%d%d%d", &s, &t, &c);            add(s, t, c);        }        printf("Case %d: %d\n", ca++, maxFlow(1, n, n, m));    }    return 0;}