【网络流基础】hdu 1532 Drainage Ditches

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题意：给出网络流的一些边，求节点1到节点n的最大流。
难度：0
题解：直接连边求最大流。
#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;#define forn(i,n) for(i=0;i<(n);i++)#define for1(i,n) for(i=1;i<=(n);i++)#define forh(i,u) for(i=head[u];i!=-1;i=edge[i].next)#define inf (1<<29)const int maxn = 222 , maxm = 555;int n , m;struct Edge {    int u,v,c,next;}edge[maxm];int E,head[maxn];int dist[maxn];int que[maxn];int sta[maxn];void init() {    E = 0; memset(head,-1,sizeof(head));}void _add(int u,int v,int c) {    edge[E].u=u;edge[E].v=v;edge[E].c=c;edge[E].next=head[u];head[u]=E++;}void addedge(int u,int v,int c) {    _add(u,v,c); _add(v,u,0);}int dinic(int s,int t) {    int ans = 0;    while(true) {        int left,right,u,v,c,i;        memset(dist,-1,sizeof(dist));        left = right = 0;        que[right ++] = s;        dist[s] = 0;        while(left < right) {            u  = que[left ++];            forh(i,u) {                u=edge[i].u;                v=edge[i].v;                c=edge[i].c;                if(c>0 && dist[v] == -1) {                    dist[v] = dist[u] + 1;                    que[right ++] = v;                    if(v == t) {                        left = right;                        break;                    }                }            }        }        if(dist[t] == -1) break;        int top = 0;        int now = s;        while(true) {            if(now != t) {                forh(i,now) {                    u=edge[i].u;                    v=edge[i].v;                    c=edge[i].c;                    if(c > 0 && dist[u] + 1 == dist[v])                        break;                }                if(i != -1) {                    sta[top ++] = i;                    now = edge[i].v;                }                else {                    if(top == 0) break;                    dist[edge[sta[--top]].v] = -1;                    now = edge[sta[top]].u;                }            }            else {                int flow = inf , ebreak;                forn(i,top)                    if(flow > edge[sta[i]].c)                        flow = edge[sta[ebreak = i]].c;                ans += flow;                forn(i,top) {                    edge[sta[i]].c -= flow;                    edge[sta[i]^1].c += flow;                }                now = edge[sta[top = ebreak]].u;            }        }    }    return ans;}int main() {    while(~scanf("%d%d",&m,&n)) {        init();        while(m--) {            int u , v , c;            scanf("%d%d%d",&u,&v,&c);            addedge(u,v,c);        }        int ans = dinic(1,n);        printf("%d\n",ans);    }    return 0;}
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