Submission #155065

#	Time	Username	Problem	Language	Result	Execution time	Memory
155065		Charis02	Homecoming (BOI18_homecoming)	C++14	100 / 100	232 ms	116740 KiB

homecoming

#include<iostream>
#define ll long long
#define rep(i,a,b) for(int i = a;i < b;i++)
#define N 2000003
#define INF 1e16

using namespace std;

ll books[N],prize[N],sum[N],n,k;
ll dp[N][2];
const ll PASSED=1,NPASSED=0;

ll get_sum(ll i,ll j)
{
    if(i == 0)
        return sum[j];

    return sum[j] - sum[i-1];
}

ll solve(int NN,int K,int A[],int B[])
{
    n = NN;
    k = K;
    rep(i,0,n)
    {
        prize[i] = A[i];
        books[i] = B[i];

        if(i == 0)
            sum[i] = books[i];
        else
            sum[i] = sum[i-1]+books[i];
    }

    /*
        if you pass class i and class j and j-i < k it is optimal to pass all classes in between.
    */

    // fix that class 0 is passed

    dp[0][PASSED] = prize[0] - get_sum(0,k-1);
    dp[0][NPASSED] = -INF;

    rep(i,1,n)
    {
        ll nextbook = i+k-1;

        // passed previous class
        ll cur = dp[i-1][PASSED];
        if(nextbook < n)
            cur -= books[nextbook];
        cur+=prize[i];
        dp[i][PASSED] = cur;

        //didn't pass previous class
        cur = dp[i-1][NPASSED];
        cur -= get_sum(i,min(n-1,nextbook)); // if we add stuff that is already in dp[i-1][NPASSED], then optimal answer isn't here since we could just pass class i-1
        cur+=prize[i];
        dp[i][PASSED] = max(dp[i][PASSED],cur);

        dp[i][NPASSED] = max(dp[i-1][NPASSED],dp[i-1][PASSED]);
    }

    ll ans = max(dp[n-1][PASSED],dp[n-1][NPASSED]);

    // fix that he didn't pass class 0

    dp[0][NPASSED] = 0;
    dp[0][PASSED] = -INF;

    rep(i,1,n)
    {
        ll nextbook = (i+k-1)%n;

        // passed previous class
        ll cur = dp[i-1][PASSED];
        cur -= books[nextbook];
        cur+=prize[i];
        dp[i][PASSED] = cur;

        //didn't pass previous class
        cur = dp[i-1][NPASSED];
        if(nextbook < i)
            cur -= get_sum(i,n-1) + get_sum(0,nextbook);
        else
            cur -= get_sum(i,nextbook);

        cur+=prize[i];
        dp[i][PASSED] = max(dp[i][PASSED],cur);

        dp[i][NPASSED] = max(dp[i-1][NPASSED],dp[i-1][PASSED]);
    }

    ans = max(ans,dp[n-1][PASSED]);
    ans = max(ans,dp[n-1][NPASSED]);

    return ans;
}

• Subtask 1: 13 / 13
• Subtask 2: 18 / 18
• Subtask 3: 31 / 31
• Subtask 4: 38 / 38