【codevs 4246】奶牛的身高 差分约束

用差分约束乱搞吧……
在那次月赛里算个水题了……
点击就送屠龙宝刀

#include <iostream>#include <cstdio>#include <algorithm>#include <cstring>#include <queue>using namespace std;const int MAXN = 100000 + 5;const int MAXM = 100000 + 5;struct edge{    int f,t,v;}l[MAXM * 2];int first[MAXN],next[MAXN * 2],tot;int dis[MAXN];bool use[MAXN];bool in[MAXN];void init(){    memset(first,0xfff,sizeof(first));    memset(use,0,sizeof(use));    memset(dis,0,sizeof(dis));    memset(in,0,sizeof(in));    tot = 0;    return;}void build(int f,int t,int v){    l[++tot] = (edge){f,t,v};    next[tot] = first[f];    first[f] = tot;    return;}queue <int> q;bool bfs(int u){    while(!q.empty())        q.pop();    q.push(u);    use[u] = true;    while(!q.empty())    {        u = q.front();        q.pop();        for(int i = first[u];i != -1;i = next[i])        {            int v = l[i].t;            if(use[v])                if(dis[v] != dis[u] + l[i].v)                    return false;            dis[v] = dis[u] + l[i].v;            if(!use[v])                q.push(v);            use[v] = true;        }    }    return true;}int T,n,m,f,t,v;int main(){    scanf("%d",&T);    while(T--)    {        init();        scanf("%d %d",&n,&m);        for(int i = 1;i <= m;i ++)        {            scanf("%d %d %d",&t,&f,&v);            build(f,t, v);            build(t,f,-v);        }        for(int i = 1;i <= n;i ++)            if(!bfs(i))            {                puts("Bessie is blind.");                goto cont;            }        puts("Bessie's eyes are good");        cont:            continue;    }    return 0;}