bzoj 1266: [AHOI2006]上学路线route

这个题可以先floyd求出最短路

在将包含原图中所有S->T最短路径的子图抽出来求最小割（就是最大流啦）

f[S][i]+f[i][j]+f[j][T] == f[S][T]代表i->j边在要求的这个子图中

#include <cstdio>
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
#define N 508
#define M 124758
#define INF 0x7ffffff

int n,m,tot1,tot2,head1[N],head2[N],f[N][N],lay[N],que[N],l,r,ans;
bool flag[N],vis[N];
struct edge
{
    int next,value,node,dist;    
}e[M*2];
struct bow
{
    int next,node,res;
}b[M];

void add1(int u,int v,int t,int c)
{
    e[++tot1].node = v;
    e[tot1].next = head1[u];
    e[tot1].value = c;
    e[tot1].dist = t;
    head1[u] = tot1;
}

void init()
{
   scanf("%d%d",&n,&m);
   for (int i = 1;i <= n;i++) 
       for (int j = 1;j <= n;j++) 
           if (i != j) f[i][j] = INF;
   for (int i = 1;i <= m;i++)
   {
       int u,v,t,c;
       scanf("%d%d%d%d",&u,&v,&t,&c);
       add1(u,v,t,c);
       add1(v,u,t,c);
       f[u][v] = f[v][u] = min(f[u][v],t);
   }
}

void floyd()
{
    for (int k = 1;k <= n;k++)
        for (int i = 1;i <= n;i++)
            for (int j = 1;j <= n;j++)
                f[i][j] = min(f[i][j],f[i][k]+f[k][j]);
}

void add2(int u,int v,int c)
{
    b[tot2].node = v;
    b[tot2].res = c;
    b[tot2].next = head2[u];
    head2[u] = tot2++;
}

void rebuild()
{
    memset(head2,255,sizeof(head2));
    for (int i = 1;i <= n;i++)
    {
        int c = head1[i];
        while (c)
        {
            if (f[1][i] + e[c].dist + f[e[c].node][n] == f[1][n])
            {
                add2(i,e[c].node,e[c].value);
                add2(e[c].node,i,0);
            }
            c = e[c].next;
        }
    }
}

bool build()
{

    memset(vis,0,sizeof(vis));
    memset(lay,255,sizeof(lay));
    l = 0; r = 1; que[1] = 1; lay[1] = 0;
    while (l < r)
    {
        int u = que[++l];
        int c = head2[u];
        while (c != -1)
        {
            if (b[c].res && lay[b[c].node] == -1) 
                lay[b[c].node] = lay[u] + 1,que[++r] = b[c].node;
            c = b[c].next;
        }
    }
    if (lay[n] == -1) return false;
    return true;
}

int find(int u,int low)
{
    if (u == n) return low;
    int ans = 0;
    int c = head2[u];
    while (c != -1 && low)
    {
        int tans;
        if (lay[b[c].node] == lay[u]+1 && (tans = find(b[c].node,min(b[c].res,low))))
        {
            b[c].res -= tans;
            b[c^1].res += tans;
            ans += tans;
            low -= tans;
        }
        c = b[c].next;
    }
    return ans;
}

void dinic()
{
    while (build())
    {
        int tans;
        while(tans = find(1,INF)) ans += tans;
    }
}

int main()
{
    init();
    floyd();
    printf("%d
",f[1][n]);
    rebuild();
    dinic();
    printf("%d
",ans);
    return 0;
}

我这个傻逼一开始数组开小了RE了还傻乎乎地跑去去问葱娘！！真他妈丢死人了！！！