luoguP1525 关押罪犯 题解(NOIP2010)(并查集反集)

P1525 关押罪犯  题目

#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<iomanip>
#include<algorithm>
#include<queue>
#include<ctime>
#define ll long long
#define rg register
#define M 100050
#define N 20050
using namespace std;

int n,m;
struct war{
    int l,r,v;
}ljl[M];
int fa[N<<1];

inline int read()
{
    int s=0,m=1;char ch=getchar();
    while(ch!='-'&&(ch<'0'||ch>'9'))ch=getchar();
    if(ch=='-')m=-1,ch=getchar();
    while(ch>='0'&&ch<='9')s=(s<<3)+(s<<1)+ch-'0',ch=getchar();
    return s*m;
}

inline bool cmp(const war &a,const war &b)
{
    return a.v>b.v;
}

int find_fa(int kk)
{
    if(fa[kk]==kk)return kk;
    else
        {
            fa[kk]=find_fa(fa[kk]);
            return fa[kk];
        }
}

void add(int k1,int k2)
{
    int fa1=find_fa(k1);
    int fa2=find_fa(k2);
    fa[fa1]=fa2;
}

int main()
{
    n=read();m=read();
    for(int i=1;i<=m;++i)
        {
            ljl[i].l=read();ljl[i].r=read();ljl[i].v=read();
        }
    sort(ljl+1,ljl+m+1,cmp);
    for(int i=1;i<=n<<1;++i)
        {
            fa[i]=i;
        }
    for(int i=1;i<=m;++i)
        {
            int f1=find_fa(ljl[i].l);
            int f2=find_fa(ljl[i].r);
            if(f1==f2)
                {
                    printf("%d
",ljl[i].v);
                    exit(0);
                }
            else
                {
                    add(ljl[i].l,ljl[i].r+n);
                    add(ljl[i].r,ljl[i].l+n);
                }
        }
    puts("0");
    return 0;
}