【HDOJ】3416 Marriage Match IV

先求SPSS。然后遍历每条边，检查是否为最短路径的边，如果是（dis[v]==dis[u]+w）则加入到网络流中。最后Dinic最大流.

 /* 3416 */
 #include <iostream>
 #include <string>
 #include <map>
 #include <queue>
 #include <set>
 #include <stack>
 #include <vector>
 #include <deque>
 #include <algorithm>
 #include <cstdio>
 #include <cmath>
 #include <ctime>
 #include <cstring>
 #include <climits>
 #include <cctype>
 #include <cassert>
 #include <functional>
 #include <iterator>
 #include <iomanip>
 using namespace std;
 //#pragma comment(linker,"/STACK:102400000,1024000")

 #define sti                set<int>
 #define stpii            set<pair<int, int> >
 #define mpii            map<int,int>
 #define vi                vector<int>
 #define pii                pair<int,int>
 #define vpii            vector<pair<int,int> >
 #define rep(i, a, n)     for (int i=a;i<n;++i)
 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 #define clr                clear
 #define pb                 push_back
 #define mp                 make_pair
 #define fir                first
 #define sec                second
 #define all(x)             (x).begin(),(x).end()
 #define SZ(x)             ((int)(x).size())
 #define lson            l, mid, rt<<1
 #define rson            mid+1, r, rt<<1|1

 const int INF = 0x1f1f1f1f;
 const int maxn = ;
 const int maxe = ;
 int head[maxn], nxt[maxe], V[maxe], F[maxe];
 int head_[maxn], nxt_[maxe], V_[maxe], W[maxe];
 int dis[maxn], pre[maxn], ID[maxn];
 bool visit[maxn];
 int n, m;

 void addEdge_(int u, int v, int w) {
     V_[m] = v;
     W[m] = w;
     nxt_[m] = head_[u];
     head_[u] = m++;
 }

 void addEdge(int u, int v, int c) {
     V[m] = v;
     F[m] = c;
     nxt[m] = head[u];
     head[u] = m++;

     V[m] = u;
     F[m] = ;
     nxt[m] = head[v];
     head[v] = m++;
 }

 void spfa(int u) {
     int v, k;
     queue<int> Q;

     memset(dis, 0x1f, sizeof(dis));
     memset(visit, false, sizeof(visit));
     Q.push(u);
     dis[u] = ;
     visit[u] = true;

     while (!Q.empty()) {
         u = Q.front();
         Q.pop();
         visit[u] = false;
         for (k=head_[u]; k!=-; k=nxt_[k]) {
             v = V_[k];
             if (dis[v] > dis[u]+W[k]) {
                 dis[v] = dis[u] + W[k];
                 if (!visit[v]) {
                     visit[v] = true;
                     Q.push(v);
                 }
             }
         }
     }
 }

 bool bfs(int s, int t) {
     queue<int> Q;
     int u, v, k;

     memset(dis, , sizeof(dis));
     Q.push(s);
     dis[s] = ;
     pre[s] = s;

     while (!Q.empty()) {
         u = Q.front();
         Q.pop();
         for (k=head[u]; k!=-; k=nxt[k]) {
             v = V[k];
             if (F[k] && !dis[v]) {
                 dis[v] = dis[u] + ;
                 pre[v] = u;
                 ID[v] = k;
                 Q.push(v);
             }
         }
     }

     return dis[t] == ;
 }

 int dfs(int u, int t, int val)  {
     if (u==t || val==)
         return val;

     int ret = , tmp;
     int v, k;

     for (k=head[u]; k!=-; k=nxt[k]) {
         v = V[k];
         if (dis[v]==dis[u]+ && F[k] && (tmp=dfs(v, t, min(val, F[k])))>) {
             F[k] -= tmp;
             F[k^] += tmp;
             ret += tmp;
             val -= tmp;
             if (val == )
                 break;
         }
     }

     return ret;
 }

 int Dinic(int s, int t) {
     int ret = , tmp;

     while () {
         if (bfs(s, t))
             break;

         tmp = dfs(s, t, INF);
         ret += tmp;
     }

     return ret;
 }

 int main() {
     ios::sync_with_stdio(false);
     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     int tt;
     int s, t, n_, m_;
     int u, v, k, w;
     int ans;

     scanf("%d", &tt);
     while (tt--) {
         scanf("%d %d", &n_, &m_);
         memset(head_, -, sizeof(head_));
         m = ;
         while (m_--) {
             scanf("%d %d %d", &u, &v, &w);
             if (u != v)
                 addEdge_(u, v, w);
         }

         scanf("%d %d", &s, &t);
         spfa(s);

         m = ;
         memset(head, -, sizeof(head));
         rep(i, , n_+) {
             for (k=head_[i]; k!=-; k=nxt_[k]) {
                 v = V_[k];
                 if (dis[v] == dis[i] + W[k]) {
                     addEdge(i, v, );
                 }
             }
         }

         ans = Dinic(s, t);
         printf("%d\n", ans);
     }

     #ifndef ONLINE_JUDGE
         printf("time = %d.\n", (int)clock());
     #endif

     return ;
 }