就是网络流的版题详情请看
https://www.cnblogs.com/qmcp/p/9686202.html
代码如下：
1 #include<cstdio>
2 #include<cmath>
3 #include<algorithm>
4 #include<cstring>
5 #include<queue>
6 using namespace std;
7 typedef long long ll;
8 const ll maxn = 1e5 + 7;
9 const ll inf = 0x7777777;
10 ll read()
11 {
12 ll a = 0,b = 1;
13 char c = getchar();
14 while(c < '0' or c > '9')
15 {
16 if(c == '-') b = -1;
17 c = getchar();
18 }
19 while(c >= '0' and c <= '9')
20 {
21 a = a * 10 + c - '0';
22 c = getchar();
23
24 }return a * b;
25 }
26 ll head[maxn],dep[maxn],cnt = -1,n,m,s,t,ans;
27 queue<ll>qq;
28 struct node
29 {
30 ll w,to,nxt;
31 }e[maxn];
32 void add(ll a1,ll b1, ll c1)
33 {
34 e[++cnt].to = b1;
35 e[cnt].nxt = head[a1];
36 e[cnt].w = c1;
37 head[a1] = cnt;
38 }
39 bool bfs()
40 {
41 while(!qq.empty()) qq.pop();
42 memset(dep,0,sizeof(dep));
43 qq.push(s);
44 dep[s] = 1;
45 while(!qq.empty())
46 {
47 ll u = qq.front();
48 qq.pop();
49 for(int i=head[u]; ~i; i=e[i].nxt)
50 {
51 if(dep[e[i].to] == 0 and e[i].w)
52 {
53 dep[e[i].to] = dep[u] + 1;
54 qq.push(e[i].to);
55 }
56 }
57 }
58 return dep[t];
59 }
60 ll dfs(ll u, ll limit)
61 {
62 if(limit == 0) return 0;
63 if(u == t)
64 {
65 return limit;
66 }
67 for(int i=head[u]; ~i; i=e[i].nxt)
68 {
69 if(e[i].w and dep[e[i].to] == dep[u] + 1)
70 {
71 ll k = dfs(e[i].to, min(limit,e[i].w));
72 if(k)
73 {
74 e[i].w -= k;
75 e[i^1].w += k;
76 return k ;
77 }
78
79 }
80 }
81 return 0;
82 }
83 int main()
84 {
85 m = read(); n = read();
86 s = 1; t = n;
87 memset(head,-1,sizeof(head));
88 for(int i=1; i<=m; i++)
89 {
90 ll p,q,z;
91 p = read();
92 q = read();
93 z = read();
94 add(p,q,z);
95 add(q,p,0);
96 }
97 while(bfs()) {
98 ll l = dfs(s,inf);
99 if(l)
100 ans+=l;
101 }
102 printf("%lld",ans);
103 return 0;
104 }