Gym - 100712H

Gym - 100712H 

tarjan无向图缩点+树上直径

#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<set>
#include<map>
#include<stack>
#include<cstring>
#define inf 2147483647
#define ls rt<<1
#define rs rt<<1|1
#define lson ls,nl,mid,l,r
#define rson rs,mid+1,nr,l,r
#define N 100010
#define For(i,a,b) for(int i=a;i<=b;i++)
#define p(a) putchar(a)
#define g() getchar()

using namespace std;
int T;
int n,m,x,y,now,Max,temp;
int dfn[N],low[N];
int cnt,col,c[N];
bool vis[N];
struct node{
    int n;
    node *next;
}*e[N];

stack<int>s;

void in(int &x){
    int y=1;
    char c=g();x=0;
    while(c<'0'||c>'9'){
        if(c=='-')y=-1;
        c=g();
    }
    while(c<='9'&&c>='0'){
        x=(x<<1)+(x<<3)+c-'0';c=g();
    }
    x*=y;
}
void o(int x){
    if(x<0){
        p('-');
        x=-x;
    }
    if(x>9)o(x/10);
    p(x%10+'0');
}

void push(int x,int y){
    node *p;
    p=new node();
    p->n=y;
    if(e[x]==NULL)
        e[x]=p;
    else{
        p->next=e[x]->next;
        e[x]->next=p;
    }
}

void tarjan(int x,int fa){
    dfn[x]=low[x]=++cnt;
    vis[x]=true;
    s.push(x);
    for(node *i=e[x];i;i=i->next){
        if(i->n==fa) continue;//无向图关键
        if(!dfn[i->n]){
            tarjan(i->n,x);
            low[x]=min(low[x],low[i->n]);
        }
        else
            if(vis[i->n])
                low[x]=min(low[x],dfn[i->n]);
    }

    if(low[x]==dfn[x]){
        col++;
        do{
            now=s.top();
            c[now]=col;
            s.pop();
            vis[now]=true;
        }while(x!=now);
    }
}

void dfs(int x,int depth){
    vis[x]=true;
    if(depth>Max){
        Max=depth;
        temp=x;
    }
    for(node *i=e[x];i;i=i->next){
        if(!vis[i->n]){
            if(c[i->n]!=c[x]) dfs(i->n,depth+1);
            else dfs(i->n,depth);
        }
    }
}

void clear(){
    cnt=0;
    Max=0;
    col=0;
    temp=0;
    memset(dfn,0,sizeof(dfn));
}

int main(){
    in(T);
    while(T--){
        clear();
        in(n);in(m);
        For(i,1,m){
            in(x);in(y);
            push(x,y);
            push(y,x);
        }
        For(i,1,n) vis[i]=false;
        tarjan(1,1);
        For(i,1,n) vis[i]=false;
        dfs(1,0);
        For(i,1,n) vis[i]=false;
        dfs(temp,0);
        o(col-1-Max);p('\n');
        For(i,1,n) e[i]=0;
    }
        
    return 0;
}