洛谷P2024 食物链 [NOI2001] 并查集

正解:并查集

解题报告:

传送门

其实没有很难(虽然我是交了三发才过的QAQ

但是一来好久没打并查集了恢复一下智力

二来看着智推里唯一一个蓝就很不爽(,,,虽然做了这题之后又补上了个蓝题QAQ

所以就做了下QwQ

先放下代码趴QAQ明天写下解法,难点在于分类讨论

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define rp(i,x,y) for(register ll i=x;i<=y;++i)
#define lowbit(x) x&(-x)

const ll N=50000+100;
ll n,k,fa[N*3],ans;

inline ll read()
{
    register char ch=getchar();register ll x=0;register bool y=1;
    while(ch!='-' && (ch>'9' || ch<'0'))ch=getchar();
    if(ch=='-')ch=getchar(),y=0;
    while(ch>='0' && ch<='9')x=(x<<1)+(x<<3)+(ch^'0'),ch=getchar();
    return y?x:-x;
}
inline ll fd(ll x){return fa[x]==x?fa[x]:fa[x]=fd(fa[x]);}

int main()
{
    n=read();k=read();rp(i,1,n*3)fa[i]=i;
    rp(i,1,k)
    {
        ll op=read();
        if(op==1)
        {
            ll x=read(),y=read();
            if(x>n || y>n){++ans;continue;}
            ll fa1=fd(x),fa2=fd(y),fa3=fd(x+n),fa4=fd(y+n),fa5=fd(x+n+n),fa6=fd(y+n+n);
            if(fa3==fa2 || fa5==fa2){++ans;continue;}
            fa[fa1]=fa2;fa[fa3]=fa4;fa[fa5]=fa6;
            continue;
        }
        ll x=read(),y=read();
        if(x>n || y>n || x==y){++ans;continue;}
        ll fa1=fd(x),fa2=fd(y),fa3=fd(x+n),fa4=fd(y+n),fa5=fd(x+n+n),fa6=fd(y+n+n);
        if(fa1==fa2 || fa5==fa2){++ans;continue;}
        fa[fa3]=fa2;fa[fa6]=fa1;fa[fa5]=fa4;
    }
    printf("%lld\n",ans);
    return 0;
}
//fax:xÒ»Àà fax+n:x³Ôʲô fax+2n:x±»³Ô 

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