bzoj3687 简单题

Posted 2020-09-15 逢山开路 遇水架桥

传送门：http://www.lydsy.com/JudgeOnline/problem.php?id=3687

【题解】

记f[i]为和为i的子集出现了几次。

那么加入一个数x，如果选择，就相当于f整体左移x；不选择就是f。那么异或起来就行了。

用bitset实现。复杂度O(n*2000000/32)

# include <bitset>
# include <stdio.h>
# include <string.h>
# include <algorithm>
// # include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
const int M = 5e5 + 10;
const int mod = 1e9+7;

# define RG register
# define ST static

int n, x, ans;
bitset<2000010> bs;

int main() {
    scanf("%d", &n);
    bs[0] = 1;
    for (int i=1; i<=n; ++i) {
        scanf("%d", &x);
        bs = (bs << x) ^ bs;
    }
    for (int i=0; i<=2000000; ++i)
        if(bs[i]) ans ^= i;
    printf("%d\n", ans);
    return 0;
}

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