洛谷P2469 星际竞速

上下界费用流比较无脑，提供一种更巧妙的费用流，无需上下界。

 #include <cstdio>
 #include <algorithm>
 #include <queue>
 #include <cstring>

 const int N = , M = , INF = 0x3f3f3f3f;

 struct Edge {
     int nex, v, c, len;
 }edge[M << ]; int top = ;

 int e[N], d[N], vis[N], pre[N], flow[N];
 std::queue<int> Q;

 inline void add(int x, int y, int z, int w) {
     top++;
     edge[top].v = y;
     edge[top].c = z;
     edge[top].len = w;
     edge[top].nex = e[x];
     e[x] = top;

     top++;
     edge[top].v = x;
     edge[top].c = ;
     edge[top].len = -w;
     edge[top].nex = e[y];
     e[y] = top;
     return;
 }

 inline bool SPFA(int s, int t) {
     memset(d, 0x3f, sizeof(d));
     d[s] = ;
     flow[s] = INF;
     vis[s] = ;
     Q.push(s);
     while(!Q.empty()) {
         int x = Q.front();
         Q.pop();
         vis[x] = ;
         for(int i = e[x]; i; i = edge[i].nex) {
             int y = edge[i].v;
             if(edge[i].c && d[y] > d[x] + edge[i].len) {
                 d[y] = d[x] + edge[i].len;
                 pre[y] = i;
                 flow[y] = std::min(flow[x], edge[i].c);
                 if(!vis[y]) {
                     vis[y] = ;
                     Q.push(y);
                 }
             }
         }
     }
     return d[t] < INF;
 }

 inline void update(int s, int t) {
     int temp = flow[t];
     while(t != s) {
         int i = pre[t];
         edge[i].c -= temp;
         edge[i ^ ].c += temp;
         t = edge[i ^ ].v;
     }
     return;
 }

 inline int solve(int s, int t, int &cost) {
     int ans = ;
     cost = ;
     while(SPFA(s, t)) {
         ans += flow[t];
         cost += flow[t] * d[t];
         update(s, t);
     }
     return ans;
 }

 int main() {
     int n, m;
     scanf("%d%d", &n, &m);
     int s = n *  + ;
     int t = s + , S = s + , T = s + , O = s + ;
     for(int i = , x; i <= n; i++) {
         scanf("%d", &x);
         add(O, i, , x);
         add(i + n, O, INF, );
         // add(i, i + n, 1, 0);
         add(S, i + n, , );
         add(i, T, , );
         add(i + n, t, , );
     }
     add(s, O, , );
     for(int i = , x, y, z; i <= m; i++) {
         scanf("%d%d%d", &x, &y, &z);
         if(x > y) {
             std::swap(x, y);
         }
         add(x + n, y, INF, z);
     }
     add(t, s, INF, );

     int ans;
     solve(S, T, ans);
     printf("%d", ans);
     return ;
 }

上下界费用流AC代码