Drainage Ditches（POJ1273+网络流+Dinic+EK）

题目链接：poj.org/problem?id=1273

题目：

题意：求最大流。

思路：测板子题，分别用Dinic和EK实现（我的板子跑得时间均为0ms）。

Dinic代码实现如下：

 #include <set>
 #include <map>
 #include <queue>
 #include <stack>
 #include <cmath>
 #include <bitset>
 #include <cstdio>
 #include <string>
 #include <vector>
 #include <cstdlib>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 using namespace std;

 typedef long long ll;
 typedef pair<ll, ll> pll;
 typedef pair<int, ll> pil;;
 typedef pair<int, int> pii;
 typedef unsigned long long ull;

 #define lson i<<1
 #define rson i<<1|1
 #define bug printf("*********\n");
 #define FIN freopen("D://code//in.txt", "r", stdin);
 #define debug(x) cout<<"["<<x<<"]" <<endl;
 #define IO ios::sync_with_stdio(false),cin.tie(0);

 const double eps = 1e-;
 const int mod = ;
 const int maxn =  + ;
 const double pi = acos(-);
 const int inf = 0x3f3f3f3f;
 const ll INF = 0x3f3f3f3f3f3f3f;

 int n, m, tot, maxflow, s, t, u, v, w;
 int head[maxn<<], d[maxn<<];

 queue<int> q;

 struct edge {
     int v, w, next;
 }ed[maxn<<];

 void addedge(int u, int v, int w) {
     ed[tot].v = v;
     ed[tot].w = w;
     ed[tot].next = head[u];
     head[u] = tot++;
     ed[tot].v = u;
     ed[tot].w = ;
     ed[tot].next = head[v];
     head[v] = tot++;
 }

 bool bfs() {
     memset(d, , sizeof(d));
     while(!q.empty()) q.pop();
     q.push(s);
     d[s] = ;
     while(!q.empty()) {
         int x = q.front(); q.pop();
         for(int i = head[x]; ~i; i = ed[i].next) {
             if(ed[i].w && !d[ed[i].v]) {
                 q.push(ed[i].v);
                 d[ed[i].v] = d[x] + ;
                 if(ed[i].v == t) return ;
             }
         }
     }
     return ;
 }

 int dinic(int x, int flow) {
     if(x == t) return flow;
     int rest = flow, k;
     for(int i = head[x]; ~i && rest; i = ed[i].next) {
         if(ed[i].w && d[ed[i].v] == d[x] + ) {
             k = dinic(ed[i].v, min(rest, ed[i].w));
             if(!k) d[ed[i].v] = ;
             ed[i].w -= k;
             ed[i^].w += k;
             rest -= k;
         }
     }
     return flow - rest;
 }

 int main() {
     //FIN;
     while(~scanf("%d%d", &m, &n)) {
         s = , t = n;
         tot = , maxflow = ;
         memset(head, -, sizeof(head));
         for(int i = ; i <= m; i++) {
             scanf("%d%d%d", &u, &v, &w);
             addedge(u, v, w);
         }
         int flow = ;
         while(bfs()) {
             while(flow = dinic(s, inf)) {
                 maxflow += flow;
             }
         }
         printf("%d\n", maxflow);
     }
     return ;
 }

EK实现如下：

 #include <set>
 #include <map>
 #include <queue>
 #include <stack>
 #include <cmath>
 #include <bitset>
 #include <cstdio>
 #include <string>
 #include <vector>
 #include <cstdlib>
 #include <cstring>
 #include <iostream>
 #include <algorithm>
 using namespace std;

 typedef long long ll;
 typedef pair<ll, ll> pll;
 typedef pair<int, ll> pil;;
 typedef pair<int, int> pii;
 typedef unsigned long long ull;

 #define lson i<<1
 #define rson i<<1|1
 #define bug printf("*********\n");
 #define FIN freopen("D://code//in.txt", "r", stdin);
 #define debug(x) cout<<"["<<x<<"]" <<endl;
 #define IO ios::sync_with_stdio(false),cin.tie(0);

 const double eps = 1e-;
 const int mod = ;
 const int maxn =  + ;
 const double pi = acos(-);
 const int inf = 0x3f3f3f3f;
 const ll INF = 0x3f3f3f3f3f3f3f;

 int n, m, u, v, w, tot, maxflow, s, t;
 int head[maxn<<], vis[maxn], incf[maxn], pre[maxn];

 struct edge {
     int v, w, next;
 }ed[maxn<<];

 void addedge(int u, int v, int w) {
     ed[tot].v = v;
     ed[tot].w = w;
     ed[tot].next = head[u];
     head[u] = tot++;
     ed[tot].v = u;
     ed[tot].w = ;
     ed[tot].next = head[v];
     head[v] = tot++;
 }

 bool bfs() {
     memset(vis, , sizeof(vis));
     queue<int> q;
     q.push(s);
     vis[s] = ;
     incf[s] = inf;
     while(!q.empty()) {
         int x = q.front();
         q.pop();
         for(int i = head[x]; i != -; i = ed[i].next) {
             if(ed[i].w) {
                 int v = ed[i].v;
                 if(vis[v]) continue;
                 incf[v] = min(incf[x], ed[i].w);
                 pre[v] = i;
                 q.push(v);
                 vis[v] = ;
                 if(v == t) return ;
             }
         }
     }
     return ;
 }

 void update() {
     int x = t;
     while(x != s) {
         int i = pre[x];
         ed[i].w -= incf[t];
         ed[i^].w += incf[t];
         x = ed[i^].v;
     }
     maxflow += incf[t];
 }

 int main() {
     //FIN;
     while(~scanf("%d%d", &m, &n)) {
         s = , t = n;
         tot = , maxflow = ;
         memset(head, -, sizeof(head));
         memset(pre, -, sizeof(pre));
         memset(incf, , sizeof(incf));
         for(int i = ; i <= m; i++) {
             scanf("%d%d%d", &u, &v, &w);
             addedge(u, v, w);
         }
         while(bfs()) update();
         printf("%d\n", maxflow);
     }
     return ;
 }