【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 = 1005;
const int maxe = 200005;
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] = 0;
    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] = 0;
    visit[u] = true;
    
    while (!Q.empty()) {
        u = Q.front();
        Q.pop();
        visit[u] = false;
        for (k=head_[u]; k!=-1; 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, 0, sizeof(dis));
    Q.push(s);
    dis[s] = 1;
    pre[s] = s;
    
    while (!Q.empty()) {
        u = Q.front();
        Q.pop();
        for (k=head[u]; k!=-1; k=nxt[k]) {
            v = V[k];
            if (F[k] && !dis[v]) {
                dis[v] = dis[u] + 1;
                pre[v] = u;
                ID[v] = k;
                Q.push(v);
            }
        }
    }
    
    return dis[t] == 0;
}

int dfs(int u, int t, int val)  {
    if (u==t || val==0)
        return val;
    
    int ret = 0, tmp;
    int v, k;
    
    for (k=head[u]; k!=-1; k=nxt[k]) {
        v = V[k];
        if (dis[v]==dis[u]+1 && F[k] && (tmp=dfs(v, t, min(val, F[k])))>0) {
            F[k] -= tmp;
            F[k^1] += tmp;
            ret += tmp;
            val -= tmp;
            if (val == 0)
                break;
        }
    }
    
    return ret;
}

int Dinic(int s, int t) {
    int ret = 0, tmp;
    
    while (1) {
        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_, -1, sizeof(head_));
        m = 0;
        while (m_--) {
            scanf("%d %d %d", &u, &v, &w);
            if (u != v)
                addEdge_(u, v, w);
        }
        
        scanf("%d %d", &s, &t);
        spfa(s);
        
        m = 0;
        memset(head, -1, sizeof(head));
        rep(i, 1, n_+1) {
            for (k=head_[i]; k!=-1; k=nxt_[k]) {
                v = V_[k];
                if (dis[v] == dis[i] + W[k]) {
                    addEdge(i, v, 1);
                }
            }
        }
        
        ans = Dinic(s, t);
        printf("%d
", ans);
    }
    
    #ifndef ONLINE_JUDGE
        printf("time = %d.
", (int)clock());
    #endif
    
    return 0;
}