hdu1856 并查集

题目链接：http://icpc.njust.edu.cn/Problem/Hdu/1856/

题目就是要求并查集中各树的大小的最大值，我们只要在根节点处存树的大小就可以，合并也是合并根节点的数，最后扫一遍即可。

代码如下：

#include<bits/stdc++.h>
using namespace std;
typedef unsigned int ui;
typedef long long ll;
typedef unsigned long long ull;
#define pf printf
#define mem(a,b) memset(a,b,sizeof(a))
#define prime1 1e9+7
#define prime2 1e9+9
#define pi 3.14159265
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
#define scand(x) scanf("%llf",&x) 
#define f(i,a,b) for(int i=a;i<=b;i++)
#define scan(a) scanf("%d",&a)
#define mp(a,b) make_pair((a),(b))
#define P pair<int,int>
#define dbg(args) cout<<#args<<":"<<args<<endl;
#define inf 0x3f3f3f3f
const int maxn=1e7+10;
int n,m,t;
inline int read(){
    int ans=0,w=1;
    char ch=getchar();
    while(!isdigit(ch)){if(ch=='-')w=-1;ch=getchar();}
    while(isdigit(ch))ans=(ans<<3)+(ans<<1)+ch-'0',ch=getchar();
    return ans*w;
}
int f[maxn],cnt[maxn],ans=0;
void init()
{
    f(i,1,maxn-1)f[i]=i;
    f(i,1,maxn-1)cnt[i]=1;
    ans=0;
}
int find(int x)
{
    if(x==f[x])return x;
    return f[x]=find(f[x]);
}
void Union(int x,int y)
{
    int fx=find(x);
    int fy=find(y);
    if(fx==fy)return ;
    else
    {
        f[fx]=fy;
        cnt[fy]+=cnt[fx];
    }
}
int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    std::ios::sync_with_stdio(false);
    while(scan(m)!=EOF)
    {
        int a,b;
        init();
        if(m==0)
        {
            pf("1
");
            continue;
        }
        int maxr=0;
        f(i,1,m)
        {
            a=read(),b=read(),Union(a,b);
            maxr=max(maxr,max(a,b));
        }
        f(i,1,maxr)ans=max(ans,cnt[i]);
        pf("%d
",ans);
    }
 }