CodeForces-1253D Harmonious Graph

传送门：CodeForces-1253D

思路分析

如果存在l-r的路径，那么说明l-[l,r]这个区间所有点都有路径
用并查集维护每一个连通块，父亲为连通块内最大的节点
依次遍历点属于哪个连通块就行了

样例输入

14 8
1 2
2 7
3 4
6 3
5 7
3 8
6 8
11 12

样例输出

1

AC代码

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>
#define ls x<<1
#define rs x<<1|1
#define fi first
#define se second
#define ll long long
#define pb push_back
#define mp make_pair
#define fun function
#define sz(x) (x).size()
#define lowbit(x) (x)&(-x)
#define all(x) (x).begin(),(x).end()
#define mem(a,b) memset(a,b,sizeof(a))

namespace FastIO {
#define BUF_SIZE 100000
#define OUT_SIZE 100000
    bool IOerror=0;
    inline char nc() {
        static char buf[BUF_SIZE],*p1=buf+BUF_SIZE,*pend=buf+BUF_SIZE;
        if(p1==pend) {
            p1=buf;
            pend=buf+fread(buf,1,BUF_SIZE,stdin);
            if(pend==p1) {
                IOerror=1;
                return -1;
            }
        }
        return *p1++;
    }
    inline bool blank(char ch) {
        return ch==' '||ch=='\n'||ch=='\r'||ch=='\t';
    }
    template<class T> inline bool read(T &x) {
        bool sign=0;
        char ch=nc();
        x=0;
        for(; blank(ch); ch=nc());
        if(IOerror)return false;
        if(ch=='-')sign=1,ch=nc();
        for(; ch>='0'&&ch<='9'; ch=nc())x=x*10+ch-'0';
        if(sign)x=-x;
        return true;
    }
    template<class T,class... U>bool read(T& h,U&... t) {
        return read(h)&&read(t...);
    }
#undef OUT_SIZE
#undef BUF_SIZE
};
using namespace std;
using namespace FastIO;
using namespace __gnu_pbds;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> rbtree;

const int INF = 0x3f3f3f3f;
const int N = 2e5+10;

int f[N];

int find(int x){
    return f[x]==x?x:f[x]=find(f[x]);
}


int main() {

#ifdef xiaofan
    freopen("1.in","r",stdin);
    freopen("1.out","w",stdout);
#endif

    int n,m;
    read(n,m);
    for(int i=1;i<=n;i++) f[i]=i;
    while(m--){
        int u,v;
        read(u,v);
        int ma=find(u);
        int mi=find(v);
        if(ma<mi) swap(ma,mi);
        if(ma!=mi) f[mi]=ma;
    }
    int ans=0;
    for(int i=1;i<=n;i++){
        int ma=find(i);
        for(int j=i;j<ma;j++){
            int mi=find(j);
            if(ma<mi) swap(ma,mi);
            if(ma!=mi){
                ans++;
                f[mi]=ma;
            }
            i++;
        }
    }
    cout<<ans<<endl;




    return 0;
}