Description
In order to get from one of the F (1 <= F <= 5,000) grazing fields (which are numbered 1..F) to another field, Bessie and the rest of the herd are forced to cross near the Tree of Rotten Apples. The cows are now tired of often being forced to take a particular path and want to build some new paths so that they will always have a choice of at least two separate routes between any pair of fields. They currently have at least one route between each pair of fields and want to have at least two. Of course, they can only travel on Official Paths when they move from one field to another. Given a description of the current set of R (F-1 <= R <= 10,000) paths that each connect exactly two different fields, determine the minimum number of new paths (each of which connects exactly two fields) that must be built so that there are at least two separate routes between any pair of fields. Routes are considered separate if they use none of the same paths, even if they visit the same intermediate field along the way. There might already be more than one paths between the same pair of fields, and you may also build a new path that connects the same fields as some other path.
Input
* Line 1: Two space-separated integers: F and R * Lines 2..R+1: Each line contains two space-separated integers which are the fields at the endpoints of some path.
Output
* Line 1: A single integer that is the number of new paths that must be built.
Sample Input
Sample Output
HINT
垃圾tarjan毁我青春这道题很好想啊,求出边双缩个点,然后答案就是(叶子节点数+1)/2因为每对点至少有一条边,所以他就可以与另外一座桥后面的联通块连边,一条边就消掉了俩剩下那个就老老实实加边打了一个小时的“边双”结果是点双知道真相的我眼泪掉下来
//MT_LI#include#include #include #include #include #include using namespace std;struct node{ int x,y,next;}a[410000],e[410000];int len,last[410000];void ins(int x,int y){ len++; a[len].x=x;a[len].y=y; a[len].next=last[x];last[x]=len;}int dfn[410000],low[440000];int v[410000],id;void tarjan(int x,int edge){ low[x]=dfn[x]=++id; for(int k=last[x];k;k=a[k].next) { int y=a[k].y; if(dfn[y]==0) { tarjan(y,k); low[x]=min(low[x],low[y]); if(low[y]>dfn[x])v[k]=v[k^1]=1; } else if((k^1)!=edge)low[x]=min(low[x],dfn[y]); }}int c[41000];int ru[41000],cnt;void dfs(int x){ c[x]=cnt; for(int k=last[x];k;k=a[k].next) { int y=a[k].y; if(c[y]||v[k])continue; dfs(y); }}int sum=0;int main(){ int n,m; scanf("%d%d",&n,&m); len=1;memset(last,0,sizeof(last)); for(int i=1;i<=m;i++) { int x,y; scanf("%d%d",&x,&y); ins(x,y);ins(y,x); } cnt=id=0; memset(dfn,0,sizeof(dfn)); for(int i=1;i<=n;i++) if(!dfn[i]) tarjan(i,0); for(int i=1;i<=n;i++) if(!c[i]) { ++cnt; dfs(i); } for(int i=2;i<=len;i+=2) if(c[a[i].x]!=c[a[i].y]) ru[c[a[i].x]]++,ru[c[a[i].y]]++; for(int i=1;i<=cnt;i++)if(ru[i]==1)sum++; printf("%d\n",(sum+1)/2); return 0;}