Barricade---hdu5889（最短路+网络流）

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<iostream>
#include<vector>
#include<queue>
#include<set>
using namespace std;
#define met(a, b) memset(a, b, sizeof(a))
#define N 100005
#define INF 0x3f3f3f3f
typedef long long LL;

struct node
{
    int v, w, d, Next;
    node(int v_=0, int w_=0, int d_=0) : v(v_), w(w_), d(d_){}
}e[N*4];

vector<vector<node> >g;///存放原图；
int n, vis[N];
int dist[N];///spfa中的从起点到i的最短距离；
int l[N];///Dinic中的分层

int Head1[N], cnt1;
void Add1(int u, int v, int w)///添加新的边；
{
    e[cnt1].v = v;
    e[cnt1].w = w;
    e[cnt1].Next = Head1[u];
    Head1[u] = cnt1++;
}

void Init()
{
    g.clear();
    g.resize(n+1);
    met(Head1, -1);
    cnt1 = 0;
    for(int i=0; i<=n; i++)
    {
        vis[i] = 0;
        dist[i] = INF;
    }
}

void spfa()
{
    dist[1] = 0;
    vis[1] = 1;
    queue<int>Q;
    Q.push(1);
    while(!Q.empty())
    {
        int p = Q.front();Q.pop();
        vis[p] = 0;
        for(int i=0, len=g[p].size(); i<len; i++)
        {
            int q = g[p][i].v;
            if(dist[q] > dist[p]+g[p][i].d)
            {
                dist[q] =  dist[p]+g[p][i].d;
                if(!vis[q])
                {
                    vis[q] = 1;
                    Q.push(q);
                }
            }
        }
    }
}


bool bfs(int s, int End)
{
    met(l, 0);
    queue<int>Q;
    Q.push(s);
    l[s] = 1;
    while(!Q.empty())
    {
        int u = Q.front();Q.pop();
        if(u == End) return true;
        for(int i=Head1[u]; i!=-1; i=e[i].Next)
        {
            int v = e[i].v;
            if(!l[v] && e[i].w)
            {
                l[v] = l[u]+1;
                Q.push(v);
            }
        }
    }
    return false;
}

int dfs(int u, int MaxFlow, int End)
{
    if(u == End)return MaxFlow;

    int uflow = 0;

    for(int j=Head1[u]; j!=-1; j=e[j].Next)
    {
        int v = e[j].v;
        if(l[v]==l[u]+1 && e[j].w)
        {
            int flow = min(e[j].w, MaxFlow-uflow);
            flow = dfs(v, flow, End);
            e[j].w -= flow;
            e[j^1].w += flow;
            uflow += flow;
            if(uflow == MaxFlow)
                break;
        }
    }
    if(uflow == 0)
        l[u] = 0;
    return uflow;
}


int Dinic()
{
    int MaxFlow = 0;
    while(bfs(1, n))
        MaxFlow += dfs(1, INF, n);
    return MaxFlow;
}

int main()
{
    int T, m, u, w, v;
    scanf("%d", &T);
    while(T--)
    {
        scanf("%d %d", &n, &m);

        Init();

        for(int i=1; i<=m; i++)
        {
            scanf("%d %d %d", &u, &v, &w);
            g[u].push_back(node(v, w, 1));
            g[v].push_back(node(u, w, 1));
        }

        spfa();///更新dist

        for(int i=1; i<=n; i++)
        {
            for(int j=0, len=g[i].size(); j<len; j++)
            {
                int p = g[i][j].v;
                if(dist[p] == dist[i] + g[i][j].d)///说明从点i到达点p的路在最短路径上；
                {
                    Add1(i, p, g[i][j].w);///建立新图；
                    Add1(p, i, 0);///注意这里是0；
                }
            }
        }

        int ans = Dinic();///求最大流即可；

        printf("%d\n", ans);
    }
    return 0;
}