P3842 [TJOI2007]线段

#include<bits/stdc++.h>
using namespace std;
int n,a[20100],b[20100],f[20100][5];
int calc(int l,int r){return abs(l-r);}
int main()
{
    cin>>n;
    for(int i=1;i<=n;i++)cin>>a[i]>>b[i];
    f[1][0]=calc(1,b[1])+calc(b[1],a[1]);
    f[1][1]=calc(1,b[1]);
    for(int i=2;i<=n;i++)
    {
    f[i][0]=min(f[i-1][1]+calc(b[i-1],b[i])+calc(a[i],b[i]),f[i-1][0]+calc(b[i],a[i-1])+calc(a[i],b[i]))+1;
    f[i][1]=min(f[i-1][1]+calc(b[i-1],a[i])+calc(a[i],b[i]),f[i-1][0]+calc(a[i],a[i-1])+calc(a[i],b[i]))+1;
    }
    cout<<min(f[n][1]+calc(b[n],n),f[n][0]+calc(a[n],n));
}