P3842 [TJOI2007] 线段

点击查看代码

#include<bits/stdc++.h>
using namespace std;

const int N=2e4+10;
int dp[N][2];
int n;
int l[N],r[N];

int main()
{
    ios::sync_with_stdio(0),cin.tie(0);
    cin>>n;

    for(int i=1;i<=n;i++){
        cin>>l[i]>>r[i];
    }

    dp[1][1]=r[1]-1;
    dp[1][0]=r[1]-1+r[1]-l[1];

    int ans=0;
    for(int i=2;i<=n;i++){
        int len=r[i]-l[i];
        dp[i][0]=min(dp[i-1][1]+abs(r[i-1]-r[i]),dp[i-1][0]+abs(r[i]-l[i-1]))+len+1;
        dp[i][1]=min(dp[i-1][1]+abs(l[i]-r[i-1]),dp[i-1][0]+abs(l[i]-l[i-1]))+len+1;
    }

    ans=min(dp[n][0]+n-l[n],dp[n][1]+n-r[n]);

    cout<<ans<<endl;

    return 0;

    
}