题解 | 宵暗的妖怪

#include <iostream>
#include<algorithm>
#include<vector>
#define ll long long
using namespace std;

int main() {
    ll n;
    cin >> n;
    vector<ll>a(n);
    vector<ll>dp(n);
    for (int i = 0; i < n; i++)cin >> a[i];
    dp[0] = 0;
    dp[1] = 0;
    if (n < 3) {
        cout << 0;
        return 0;
    }
    dp[2] = a[1];
    if (n < 4) {
        cout << dp[n-1];
        return 0;
    }
    dp[3] = max(dp[2], a[2]);
    if (n < 5) {
        cout << dp[n-1];
        return 0;
    }
    dp[4] = max(dp[3], a[3]);
    if (n < 6) {
        cout << dp[n-1];
        return 0;
    }
    for (int i = 5; i < n; i++) {

        dp[i] = max(dp[i - 1], dp[i - 3] + a[i - 1]);
    }
    cout << dp[n - 1] << endl;
    return 0;
}