[Luogu] P1374 最大约数和

Luogu P1734 最大约数和

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传送门

读入S，预处理(1)到(S)之间所有数的约数和，然后直接跑一个(O(n^2))的(01)背包即可。

#include <algorithm>
#include <cstdio>
const int MAXN = 1001;
int n, rslt;
int c[MAXN], f[MAXN];
inline int solve(int now) {
    int ans(0);
    for (int i = 1; i < now; ++i)
        if(!(now % i)) ans = ans + i;
    return ans;
}
int main() {
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i) 
        c[i] = solve(i);
    for (int i = 1; i <= n; ++i)
        for (int j = n; j >= i; --j)
            f[j] = std::max(f[j], f[j - i] + c[i]), rslt = std::max(rslt, f[j]);
    printf("%d
", f[n]);
    return 0;
}