AC题解

#include<bits/stdc++.h>
#define reg register int
#define il inline
#define fi first
#define se second
#define mk(a,b) make_pair(a,b)
#define numb (ch^'0')
using namespace std;
typedef long long ll;
template<class T>
il void rd(T &x){
    char ch;x=0;bool fl=false;
    while(!isdigit(ch=getchar()))(ch=='-')&&(fl=true);
    for(x=numb;isdigit(ch=getchar());x=x*10+numb);
    (fl==true)&&(x=-x);
}
template<class T>il void output(T x){if(x/10)output(x/10);putchar(x%10+'0');}
template<class T>il void ot(T x){if(x<0) putchar('-'),x=-x;output(x);putchar(' ');}
template<class T>il void prt(T a[],int st,int nd){for(reg i=st;i<=nd;++i) ot(a[i]);putchar('\n');}
namespace Solution{
    const int N=1e5+5;
    const int mod=1e9+7;
    int n;
    int u[N],d[N];
    ll a[N],sum[N];
    int h[N];
    vector<int>dele[N];
    int main(){
        rd(n);
        int x,y;
        for(reg i=1;i<=n;++i){
            rd(x);rd(y);
            ++x;++y;h[x]=y;
        }
        int mx=0;
        for(reg i=n;i>=1;--i){
            mx=max(mx,h[i]);
            u[i]=mx;
        }
        int mi=n+233;
        for(reg i=1;i<=n;++i){
            mi=min(mi,h[i]);
            d[i]=mi;dele[d[i]-1].push_back(i);
        }
        for(reg i=1;i<=n;++i){
            ++a[d[i]];--a[u[i]+1];
        }
        for(reg i=1;i<=n;++i){
            a[i]+=a[i-1];
        }
        for(reg i=n;i>=1;--i){
            sum[i]=sum[i+1]+a[i];
        }
        ll ans=0,tot=0;
        ll len=0;
        for(reg i=n;i>=1;--i){
            for(reg j=0;j<(int)dele[i].size();++j){
                int now=dele[i][j];
                len+=u[now]-d[now]+1;
                tot-=sum[i+1]-len;
            }
            ans=(ans+tot)%mod;
            tot=tot+(a[i]-1)*a[i]/2;
        }
        cout<<ans;
        return 0;
    }
}
signed main(){
    Solution::main(); // Leetcode做过，CV过来的框架，懒得改了
    return 0;
}