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。。。
#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; }