比賽補題

A. elective

https://noip.ac/rs/show_problem/3631

巨大簡單的一道題，$ n \leq 20 $ 直接 $ 2 ^ {n} $ 列舉選的情況，每次判斷是否更優並記錄即可。

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<vector>
#include<queue>
typedef double db;
using std::pair;
using std::make_pair;
long long n, a[25], p[25];
template <class I> inline void read(I &x){
    x = 0; int f = 1; char ch;
    do { ch = getchar(); if(ch == '-') f = -1; } while(ch < '0' || ch > '9');
    do { x = (x << 1) + (x << 3) + (ch ^ 48); ch = getchar(); } while(ch >= '0' && ch <= '9');
    x *= f; return;
}
int main(){
    read(n);
    for(int i = 1; i <= n; ++i) read(a[i]);
    for(int i = 1; i <= n; ++i) read(p[i]);
    long long ans = -1, now = 0;
    double P = 1.00;
    for(int i = 0; i < (1 << n); ++i){
        P = 1.00, now = 0;
        // std::cout << i << '\n';
        for(int j = 0; j < n; ++j){
            if(i & (1 << j)) P *= ((double)p[j + 1] / 10.0), now += a[j + 1];
        }
        // if(i == 9) std::cout << p << '\n';
        if(P >= 0.5) ans = std::max(ans, now);
    }
    printf("%lld\n", ans);
    return 0;
}
 

B. seq

https://noip.ac/rs/show_problem/3632

C. tree

https://noip.ac/rs/show_problem/3633

D. graph

https://noip.ac/rs/show_problem/3634