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：

  1 #include <set>
  2 #include <map>
  3 #include <queue>
  4 #include <stack>
  5 #include <cmath>
  6 #include <bitset>
  7 #include <cstdio>
  8 #include <string>
  9 #include <vector>
 10 #include <cstdlib>
 11 #include <cstring>
 12 #include <iostream>
 13 #include <algorithm>
 14 using namespace std;
 15 
 16 typedef long long ll;
 17 typedef pair<ll, ll> pll;
 18 typedef pair<int, ll> pil;;
 19 typedef pair<int, int> pii;
 20 typedef unsigned long long ull;
 21 
 22 #define lson i<<1
 23 #define rson i<<1|1
 24 #define bug printf("*********\n");
 25 #define FIN freopen("D://code//in.txt", "r", stdin);
 26 #define debug(x) cout<<"["<<x<<"]" <<endl;
 27 #define IO ios::sync_with_stdio(false),cin.tie(0);
 28 
 29 const double eps = 1e-8;
 30 const int mod = 10007;
 31 const int maxn = 200 + 7;
 32 const double pi = acos(-1);
 33 const int inf = 0x3f3f3f3f;
 34 const ll INF = 0x3f3f3f3f3f3f3f;
 35 
 36 
 37 int n, m, tot, maxflow, s, t, u, v, w;
 38 int head[maxn<<1], d[maxn<<1];
 39 
 40 queue<int> q;
 41 
 42 struct edge {
 43     int v, w, next;
 44 }ed[maxn<<1];
 45 
 46 void addedge(int u, int v, int w) {
 47     ed[tot].v = v;
 48     ed[tot].w = w;
 49     ed[tot].next = head[u];
 50     head[u] = tot++;
 51     ed[tot].v = u;
 52     ed[tot].w = 0;
 53     ed[tot].next = head[v];
 54     head[v] = tot++;
 55 }
 56 
 57 bool bfs() {
 58     memset(d, 0, sizeof(d));
 59     while(!q.empty()) q.pop();
 60     q.push(s);
 61     d[s] = 1;
 62     while(!q.empty()) {
 63         int x = q.front(); q.pop();
 64         for(int i = head[x]; ~i; i = ed[i].next) {
 65             if(ed[i].w && !d[ed[i].v]) {
 66                 q.push(ed[i].v);
 67                 d[ed[i].v] = d[x] + 1;
 68                 if(ed[i].v == t) return 1;
 69             }
 70         }
 71     }
 72     return 0;
 73 }
 74 
 75 int dinic(int x, int flow) {
 76     if(x == t) return flow;
 77     int rest = flow, k;
 78     for(int i = head[x]; ~i && rest; i = ed[i].next) {
 79         if(ed[i].w && d[ed[i].v] == d[x] + 1) {
 80             k = dinic(ed[i].v, min(rest, ed[i].w));
 81             if(!k) d[ed[i].v] = 0;
 82             ed[i].w -= k;
 83             ed[i^1].w += k;
 84             rest -= k;
 85         }
 86     }
 87     return flow - rest;
 88 }
 89 
 90 int main() {
 91     //FIN;
 92     while(~scanf("%d%d", &m, &n)) {
 93         s = 1, t = n;
 94         tot = 0, maxflow = 0;
 95         memset(head, -1, sizeof(head));
 96         for(int i = 1; i <= m; i++) {
 97             scanf("%d%d%d", &u, &v, &w);
 98             addedge(u, v, w);
 99         }
100         int flow = 0;
101         while(bfs()) {
102             while(flow = dinic(s, inf)) {
103                 maxflow += flow;
104             }
105         }
106         printf("%d\n", maxflow);
107     }
108     return 0;
109 }

 

EK实现如下：

  1 #include <set>
  2 #include <map>
  3 #include <queue>
  4 #include <stack>
  5 #include <cmath>
  6 #include <bitset>
  7 #include <cstdio>
  8 #include <string>
  9 #include <vector>
 10 #include <cstdlib>
 11 #include <cstring>
 12 #include <iostream>
 13 #include <algorithm>
 14 using namespace std;
 15 
 16 typedef long long ll;
 17 typedef pair<ll, ll> pll;
 18 typedef pair<int, ll> pil;;
 19 typedef pair<int, int> pii;
 20 typedef unsigned long long ull;
 21 
 22 #define lson i<<1
 23 #define rson i<<1|1
 24 #define bug printf("*********\n");
 25 #define FIN freopen("D://code//in.txt", "r", stdin);
 26 #define debug(x) cout<<"["<<x<<"]" <<endl;
 27 #define IO ios::sync_with_stdio(false),cin.tie(0);
 28 
 29 const double eps = 1e-8;
 30 const int mod = 10007;
 31 const int maxn = 200 + 7;
 32 const double pi = acos(-1);
 33 const int inf = 0x3f3f3f3f;
 34 const ll INF = 0x3f3f3f3f3f3f3f;
 35 
 36 int n, m, u, v, w, tot, maxflow, s, t;
 37 int head[maxn<<1], vis[maxn], incf[maxn], pre[maxn];
 38 
 39 struct edge {
 40     int v, w, next;
 41 }ed[maxn<<1];
 42 
 43 void addedge(int u, int v, int w) {
 44     ed[tot].v = v;
 45     ed[tot].w = w;
 46     ed[tot].next = head[u];
 47     head[u] = tot++;
 48     ed[tot].v = u;
 49     ed[tot].w = 0;
 50     ed[tot].next = head[v];
 51     head[v] = tot++;
 52 }
 53 
 54 bool bfs() {
 55     memset(vis, 0, sizeof(vis));
 56     queue<int> q;
 57     q.push(s);
 58     vis[s] = 1;
 59     incf[s] = inf;
 60     while(!q.empty()) {
 61         int x = q.front();
 62         q.pop();
 63         for(int i = head[x]; i != -1; i = ed[i].next) {
 64             if(ed[i].w) {
 65                 int v = ed[i].v;
 66                 if(vis[v]) continue;
 67                 incf[v] = min(incf[x], ed[i].w);
 68                 pre[v] = i;
 69                 q.push(v);
 70                 vis[v] = 1;
 71                 if(v == t) return 1;
 72             }
 73         }
 74     }
 75     return 0;
 76 }
 77 
 78 void update() {
 79     int x = t;
 80     while(x != s) {
 81         int i = pre[x];
 82         ed[i].w -= incf[t];
 83         ed[i^1].w += incf[t];
 84         x = ed[i^1].v;
 85     }
 86     maxflow += incf[t];
 87 }
 88 
 89 int main() {
 90     //FIN;
 91     while(~scanf("%d%d", &m, &n)) {
 92         s = 1, t = n;
 93         tot = 0, maxflow = 0;
 94         memset(head, -1, sizeof(head));
 95         memset(pre, -1, sizeof(pre));
 96         memset(incf, 0, sizeof(incf));
 97         for(int i = 1; i <= m; i++) {
 98             scanf("%d%d%d", &u, &v, &w);
 99             addedge(u, v, w);
100         }
101         while(bfs()) update();
102         printf("%d\n", maxflow);
103     }
104     return 0;
105 }

 

posted @ 2018-08-03 18:25  Dillonh  阅读(206)  评论(0)  编辑  收藏  举报