Educational Codeforces Round 46 (Rated for Div. 2) B. Light It Up

Bryce1010模板

http://codeforces.com/problemset/problem/1000/B

思路：先用两个数组sumon[]和sumoff[]将亮着的灯和灭的灯累计一下。

然后从左到右扫描插入一个开关，取得到的最大值。

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

#define ll long long
const int MAXN=1e5+10;
ll sumon[MAXN];
ll sumoff[MAXN];
ll a[MAXN];
int main()
{
    ll n,m;
    cin>>n>>m;
    int i;
    for(i=1;i<=n;i++)
    {
        cin>>a[i];
        if(i&1)
        {
            sumon[i]=sumon[i-2]+a[i]-a[i-1];
            sumoff[i]=sumoff[i-1];
            //cout<<"on:"<<sumon[i];
        }
        else
        {
            sumoff[i]=sumoff[i-2]+a[i]-a[i-1];
            sumon[i]=sumon[i-1];
            //cout<<"off:"<<sumoff[i];
        }
    }
    //i++;
    if(n&1)
    {
        sumoff[i]=sumoff[i-2]+m-a[i-1];
        sumon[i]=sumon[i-1];
        //cout<<"i-2"<<sumoff[i-2];
        //cout<<"off:"<<sumoff[i];
    }
    else
    {
        sumon[i]=sumon[i-2]+m-a[i-1];
        sumoff[i]=sumoff[i-1];
        //cout<<"on:"<<sumon[i];
    }
    //cout<<endl;
    ll maxlit=-1;
    ll lit;
    maxlit=sumon[n+1];
    for(i=1;i<=n+1;i++)
    {
        lit=-1;
        if(i&1)
        {
            lit=sumon[i]-1+sumoff[n+1]-sumoff[i-1];
            maxlit=max(maxlit,lit);
        }
        else
        {
            lit=sumon[i-1]+sumoff[n+1]-sumoff[i-1]-1;
            maxlit=max(lit,maxlit);
        }
    }
    cout<<maxlit<<endl;
    return 0;
}