Codeforces 788C The Great Mixing

The Great Mixing

化简一下公式后发现， 问题变成了， 取最少多少数能使其和为1, bitset优化一下背包就好啦。

题解中介绍了一种bfs的方法没， 感觉比较巧妙。

#include<bits/stdc++.h>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ull unsigned long long

using namespace std;

const int N =  + ;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + ;
const double eps = 1e-;
const double PI = acos(-);

int n, k, a[N];
bitset<> dp[N];

int main() {
    scanf("%d%d", &n, &k);
    for(int i = ; i <= k; i++) scanf("%d", &a[i]);
    for(int i = ; i <= k; i++) {
        if(a[i] == n) {
            puts("");
            return ;
        }
        a[i] -= n;
    }
    sort(a + , a +  + k);
    k = unique(a + , a +  + k) - a - ;
    dp[][] = ;
    for(int i = ; i <= ; i++) {
        for(int j = ; j <= k; j++) {
            if(a[j] >= ) dp[i] |= dp[i - ] << a[j];
            else dp[i] |= dp[i - ] >> (-a[j]);
            if(dp[i][]) {
                printf("%d\n", i);
                return ;
            }
        }
    }
    puts("-1");
    return ;
}

/*
*/