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P4799 [CEOI2015 Day2]世界冰球锦标赛(折半搜索)

飞进科技 2022-04-18 阅读 29
算法

P4799 [CEOI2015 Day2]世界冰球锦标赛icon-default.png?t=M3C8https://www.luogu.com.cn/problem/P4799

#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <cstring>
#include <set>
#include <cmath>
#include <map>
#include <cstdlib>
#include <deque>
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
const int MN = 65005;
const int MAXN = 1000010;
const int INF = 0x3f3f3f3f;
#define IOS ios::sync_with_stdio(false)
#define lowbit(x) ((x)&(-x))

int n;
ll m;
ll s[MAXN];

void dfs(int st, int ed, ll sum, vector<ll> &v) {
	if (sum > m) {
		return;
	}
	if (st > ed) {
		v.push_back(sum);
		return;
	}
	dfs(st + 1, ed, sum + s[st], v);
	dfs(st + 1, ed, sum, v);
}

int main() {
	scanf("%d %lld", &n, &m);
	for (int i = 1; i <= n; i++) {
		scanf("%lld", s + i);
	}
	vector<ll> a;
	vector<ll> b;
	dfs(1, n / 2, 0, a);
	dfs(n / 2 + 1, n, 0, b);
	ll ans = 0;
	sort(b.begin(), b.end());
	for (auto t : a) {
		ans += upper_bound(b.begin(), b.end(), m - t) - b.begin();
	}
	printf("%lld", ans);
	return 0;
}
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