POJ1273【网络流】

#include <iostream> #include <cstring> #include <cstdio> #include <algorithm> #include <queue> #include <vector> using namespace std; const int maxnE = 1e6 + 7; const int maxn  = 1e5 + 7; const int maxnQ = 1e6 + 7; const int inf   = 0x3f3f3f3f; struct edge { int v;///弧尾 int cap;///容量 int nxt;///指向下一条从同一个弧头出发的弧 }e[maxnE]; int head[maxn],cnt; int d[maxn],cur[maxn],pre[maxn],num[maxn]; int source,sink;///超级源、超级汇 int nv;///编号修改的上限 int n,m;

queue <int> q; void add(int u, int v, int capacity) {
    e[cnt].v = v;
    e[cnt].cap = capacity;
    e[cnt].nxt = head[u];
    head[u] = cnt++; //正向边  e[cnt].v = u;
    e[cnt].cap = 0;
    e[cnt].nxt = head[v];
    head[v] = cnt++; //反向边 } void rev_bfs() {///反向bfs memset(num, 0, sizeof(num));
    memset(d, -1, sizeof(d));
    d[sink] = 0;///超级汇直接标记 num[0] = 1;
    q.push(sink); while(!q.empty()) { int u = q.front();
        q.pop(); for(int i = head[u]; ~i; i = e[i].nxt) { int v = e[i].v; if(~d[v]) continue;///已经标过号 d[v] = d[u] + 1;
            q.push(v);
            num[d[v]]++;
        }
    }
} int ISAP() {
    memcpy(cur, head, sizeof(cur));///当前弧优化  rev_bfs(); int flow = 0, u = pre[source] = source; int i; while(d[sink] < nv) {///最长的一条链上，最大的下标是nv-1，如果大于等于nv说明已断层 //printf("flow:%d\n",flow); if(u == sink) {///如果找到一条增广路，则沿着此条路修改flow int f = inf, neck; for(i = source; i != sink; i = e[cur[i]].v) {///修改流量 if(f > e[cur[i]].cap) {
                    f = e[cur[i]].cap;///不断减少所需要的流量 neck = i;///记录回退点，不用回到起点再找  }
            } for(i = source; i != sink; i = e[cur[i]].v) {///修改流量 e[cur[i]].cap -= f;
                e[cur[i] ^ 1].cap += f;
            }
            flow += f;
            u = neck;///回退  } for(i = cur[u]; ~i; i = e[i].nxt) { if(d[e[i].v] + 1 == d[u] && e[i].cap) break;
        } if(~i) { //如果存在可行的增广路 cur[u] = i;
            pre[e[i].v] = u;
            u = e[i].v;
        } else {///否则回退，重新找增广路 if(0 == (--num[d[u]])) break; int mind = nv; for(i = head[u]; ~i; i = e[i].nxt) { if(e[i].cap && mind > d[e[i].v]) {///寻找可以增广的最小下标 cur[u] = i;
                    mind = d[e[i].v];
                }
            }
            d[u] = mind + 1;
            num[d[u]]++;
            u = pre[u];///回退  }
    } return flow;
} void init() {///初始化 memset(head, -1, sizeof(head));
    cnt = 0;
} void solve()
{ int u,v,c;
    init(); for(int i = 0; i < m; ++i) {
        scanf("%d %d %d",&u, &v, &c);
        add(u,v,c);
    }
    source = 1, sink = n, nv = sink + 1;
    printf("%d\n",ISAP());
} int main()
{ while(scanf("%d %d", &m, &n) != EOF) {
        solve();
    } return 0;
}