洛谷P3376 【模板】网络最大流

洛谷P3376 【模板】网络最大流

 

 1 #include<bits/stdc++.h> 
 2 #define LL long long  
 3 #define GG int 
 4 #define For(i, j, k) for(int i=j; i<=k; i++) 
 5 #define Dow(i, j, k) for(int i=j; i>=k; i--) 
 6 using namespace std; 
 7 inline GG read() {
 8     GG x = 0, f = 1; 
 9     char ch = getchar(); 
10     while(ch<'0'||ch>'9') { if(ch=='-') f = -1; ch = getchar(); } 
11     while(ch>='0'&&ch<='9') { x = x*10+ch-48; ch = getchar(); } 
12     return x * f; 
13 }
14 inline void write(GG x) {
15     if(x<0) putchar('-'), x = -x; 
16     if(x>9) write(x/10); 
17     putchar(x%10+48);  
18 }
19 inline void writeln(GG x) {
20     write(x); puts(""); 
21 }
22 
23 const int N = 10011, M = 100011, INF = 1e9; 
24 int n, m, S, T, nedge; 
25 struct edge{
26     int to, pre, v; 
27 }e[M*2]; 
28 int head[N], dep[N], cur[N];  
29 
30 inline void add(int x, int y, int v) {
31     e[++nedge].to = y; 
32     e[nedge].pre = head[x]; 
33     e[nedge].v = v;   
34     head[x] = nedge; 
35 }
36 
37 inline void init() {
38     n = read(); m = read(); S = read(); T = read(); 
39     nedge = -1; 
40     memset(head, -1, sizeof(head)); 
41     For(i, 1, m) {
42         int x = read(), y = read(), v = read(); 
43         add(x, y, v); add(y, x, 0); 
44     }
45 }
46 
47 int dfs(int u, int dist) {
48     if(u == T) return dist; 
49     for(int& i=cur[u]; i!=-1; i=e[i].pre) {
50         int v = e[i].to; 
51         if(e[i].v>0 && dep[v]==dep[u]+1) {          //    >
52             int flow = dfs(v, min(e[i].v, dist));
53             if(flow>0) {
54                 e[i].v -= flow; 
55                     e[i^1].v += flow; 
56                 return flow; 
57             }
58         }
59     }
60     return 0; 
61 }
62 
63 inline int bfs() {
64     For(i, 0, n) dep[i] = 0; 
65     queue<int> Q; 
66     Q.push(S); dep[S] = 1; 
67     
68     while(!Q.empty()) {
69         int u = Q.front(); Q.pop(); 
70         for(int i=head[u]; i!=-1; i=e[i].pre) {
71             int v = e[i].to; 
72             if(e[i].v>0 && dep[v]==0) {
73                 dep[v] = dep[u]+1; 
74                 Q.push(v); 
75             }
76         }
77     }
78     if(dep[T]==0) 
79         return 0; 
80     else 
81         return 1; 
82 }
83 
84 inline void Dinic() {
85     int ans = 0; 
86     while(bfs()) {
87         For(i, 1, n) cur[i] = head[i]; 
88         while(int d=dfs(S, INF)) 
89             ans += d; 
90     }
91     writeln(ans); 
92 }
93 
94 int main() { 
95     init(); 
96     Dinic();
97 }

 

posted @ 2018-04-08 10:13  third2333  阅读(153)  评论(0编辑  收藏  举报