hdu 5889 Barricade

大意：1为源点，n为汇点，在图的最短路上，跑网络流

题是很水，可是在跑完最短路上，怎么处理最短路的边使得等会跑网络流的时候只在最短路的边上跑，我试了好几种方法都感觉不太好处理

最后突然恍然大悟，跑完最短路后，，直接从汇点往源点跑网络流也是一样的效果啊

最近才刚学网络流，都敲了一遍

第一种是用EK做的，，，

第二种是用Dinic做的

听说此题会卡isap，，以后试试。。

#include<iostream>//EK得做法#include<cstdio>#include<math.h>#include<algorithm>#include<map>#include<set>#include<stack>#include<queue>#include<string.h>#include<cstring>#include<vector>using namespace std;#define INF 0x3f3f3f3f#define INFLL 0x3f3f3f3f3f3f3f3f#define FIN freopen("input.txt","r",stdin)#define mem(x,y) memset(x,y,sizeof(x))typedef unsigned long long ULL;typedef long long LL;#define MX 1111#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1typedef pair<pair<int,int>,int> PIII;typedef pair<int,int> PII;int n,m,head[MX],rear;int vis[MX],path[MX],d[MX];int arr[MX];struct Edge {    int from,to,flow,nxt;} edge[22222];void edge_init() {    rear=0;    mem(head,-1);}void edge_add(int a,int b,int c) {    edge[rear].from=a;    edge[rear].to=b;    edge[rear].flow=c;    edge[rear].nxt=head[a];    head[a]=rear++;}void bfs(int s) {    mem(vis,0);    queue<int> my;    arr[s] = 0;    my.push(s);    vis[s]=1;    while(!my.empty()) {        int u = my.front();        my.pop();        for(int i = head[u]; ~i; i = edge[i].nxt) {            int v = edge[i].to;            if(vis[v]) continue;            vis[v]=1;            arr[v] = arr[u] + 1;            my.push(v);        }    }}int EK(int s,int t) {    int ans=0;    while(1) {        mem(vis,0);        d[s]=INF;        queue<int> my;        my.push(s);        vis[s]=1;        int flag=0;        while(!my.empty()) {            int u=my.front();            my.pop();            if(u==t) {                flag=1;                break;            }            for(int i=head[u]; ~i; i=edge[i].nxt) {                int v=edge[i].to;                if(!edge[i].flow||vis[v]||arr[u]!=arr[v]+1) continue;                path[v]=i;                d[v]=min(edge[i].flow,d[u]);                my.push(v);                vis[v]=1;            }        }        if(flag) {            ans+=d[t];            for(int i=t; i!=s; i=edge[path[i]].from) {                edge[path[i]].flow-=d[t];                edge[path[i]^1].flow+=d[t];            }        } else break;    }    return ans;}int main() {    int _;    scanf("%d",&_);    while(_--) {        scanf("%d%d",&n,&m);        edge_init();        for(int i=1; i<=m; i++) {            int a,b,c;            scanf("%d%d%d",&a,&b,&c);            edge_add(a,b,c);            edge_add(b,a,c);        }        bfs(1);        printf("%d\n",EK(n,1));    }    return 0;}

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#include<cstdio>//Dinic得做法#include<math.h>#include<algorithm>#include<map>#include<set>#include<stack>#include<queue>#include<string.h>#include<cstring>#include<vector>using namespace std;#define INF 0x3f3f3f3f#define INFLL 0x3f3f3f3f3f3f3f3f#define FIN freopen("input.txt","r",stdin)#define mem(x,y) memset(x,y,sizeof(x))typedef unsigned long long ULL;typedef long long LL;#define MX 1111#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1typedef pair<pair<int,int>,int> PIII;typedef pair<int,int> PII;int n,m,head[MX],rear;int vis[MX],cur[MX],d[MX];int arr[MX];struct Edge{    int to,flow,nxt;} edge[22222];void edge_init(){    rear=0;    mem(head,-1);}void edge_add(int a,int b,int c){    edge[rear].to=b;    edge[rear].flow=c;    edge[rear].nxt=head[a];    head[a]=rear++;}void bfs(int s){    mem(vis,0);    queue<int> my;    arr[s] = 0;    my.push(s);    vis[s]=1;    while(!my.empty())    {        int u = my.front();        my.pop();        for(int i = head[u]; ~i; i = edge[i].nxt)        {            int v = edge[i].to;            if(vis[v]) continue;            vis[v]=1;            arr[v] = arr[u] + 1;            my.push(v);        }    }}bool BFS(int s,int t){    mem(vis,0);    queue<int> my;    my.push(s);    vis[s]=1;    d[s]=0;    d[t]=-1;    while(!my.empty())    {        int u=my.front();        my.pop();        for(int i=head[u]; ~i; i=edge[i].nxt)        {            int v=edge[i].to;            if(arr[u]!=arr[v]+1||vis[v]||!edge[i].flow) continue;            d[v]=d[u]+1;            vis[v]=1;            my.push(v);        }    }    return d[t]!=-1;}int DFS(int x,int t,int a){    if(x==t||a==0) return a;    int flow=0,f;    for(int &i=cur[x]; ~i; i=edge[i].nxt)    {        int v=edge[i].to;        if(d[v]==d[x]+1&&arr[x]==arr[v]+1&&(f=DFS(v,t,min(a,edge[i].flow)))>0)        {            edge[i].flow-=f;            edge[i^1].flow+=f;            flow+=f;            a-=f;            if(a==0) break;        }    }    return flow;}int Dinic(int s,int t){    int flow=0;    while(BFS(s,t))    {        memcpy(cur,head,sizeof(head));        flow+=DFS(s,t,INF);    }    return flow;}int main(){    FIN;    int _;    scanf("%d",&_);    while(_--)    {        scanf("%d%d",&n,&m);        edge_init();        for(int i=1; i<=m; i++)        {            int a,b,c;            scanf("%d%d%d",&a,&b,&c);            edge_add(a,b,c);            edge_add(b,a,c);        }        bfs(1);        printf("%d\n",Dinic(n,1));    }    return 0;}