hdu 4738 桥

题目：还是自己看题目吧

trick：当不连通时不需要人去炸。否则，当桥的费用为0时当然需要一个人去炸。。。

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#include <set> #include <map> #include <list> #include <cmath> #include <queue> #include <stack> #include <string> #include <vector> #include <cstdio> #include <cstring> #include <iostream> #include <algorithm>   using namespace std;   typedef long long ll; typedef unsigned long long ull;   #define debug puts("here") #define rep(i,n) for(int i=0;i<n;i++) #define rep1(i,n) for(int i=1;i<=n;i++) #define REP(i,a,b) for(int i=a;i<=b;i++) #define foreach(i,vec) for(unsigned i=0;i<vec.size();i++) #define pb push_back #define RD(n) scanf("%d",&n) #define RD2(x,y) scanf("%d%d",&x,&y) #define RD3(x,y,z) scanf("%d%d%d",&x,&y,&z) #define RD4(x,y,z,w) scanf("%d%d%d%d",&x,&y,&z,&w) #define All(vec) vec.begin(),vec.end() #define MP make_pair #define PII pair<int,int> #define PQ priority_queue #define cmax(x,y) x = max(x,y) #define cmin(x,y) x = min(x,y) #define Clear(x) memset(x,0,sizeof(x)) /*   #pragma comment(linker, "/STACK:1024000000,1024000000")   int size = 256 << 20; // 256MB char *p = (char*)malloc(size) + size; __asm__("movl %0, %%esp\n" :: "r"(p) );   */   char IN; bool NEG; inline void Int(int &x){     NEG = 0;     while(!isdigit(IN=getchar()))         if(IN=='-')NEG = 1;     x = IN-'0';     while(isdigit(IN=getchar()))         x = x*10+IN-'0';     if(NEG)x = -x; } inline void LL(ll &x){     NEG = 0;     while(!isdigit(IN=getchar()))         if(IN=='-')NEG = 1;     x = IN-'0';     while(isdigit(IN=getchar()))         x = x*10+IN-'0';     if(NEG)x = -x; }   /******** program ********************/   const int MAXN = 1005; const int INF = 1e9;   int low[MAXN],dfn[MAXN],dep; int po[MAXN],tol; int best;   struct Edge{     int y,cost,id,next; }edge[MAXN*MAXN<<1];   void add(int x,int y,int cost,int id){     edge[++tol].y = y;     edge[tol].cost = cost;     edge[tol].id = id;     edge[tol].next = po[x];     po[x] = tol; }   void dfs(int x,int fid){     dfn[x] = low[x] = ++ dep;     for(int i=po[x];i;i=edge[i].next){         int y = edge[i].y;         int id = edge[i].id;         if(id==fid)continue;         if(!dfn[y]){             dfs(y,id);             cmin(low[x],low[y]);             if(low[y]>dfn[x]){                 if(edge[i].cost<best)                     best = edge[i].cost;             }         }else cmin(low[x],dfn[y]);     } }   int main(){   #ifndef ONLINE_JUDGE     freopen("sum.in","r",stdin);     //freopen("sum.out","w",stdout); #endif       int size = 256 << 20; // 256MB     char *p = (char*)malloc(size) + size;     __asm__("movl %0, %%esp\n" :: "r"(p) );       int n,m,x,y,cost;     while(RD2(n,m),n||m){         Clear(po);         tol = 0;         rep1(i,m){             RD3(x,y,cost);             if(x>n||y>n)continue;             add(x,y,cost,i);             add(y,x,cost,i);         }           dep = 0;         Clear(dfn);         best = INF;         int ok = 0;           rep1(i,n)             if(!dfn[i]){                 ok ++;                 dfs(i,0);             }         if(best==0)best = 1;         if(ok>1)best = 0;         printf("%d\n",best==INF?-1:best);     }       return 0; }