【CF550B Preparing Olympiad】题解

题目链接

由于 $n\leqslant 15$，所以我们可以直接枚举每条题目选或不选，最后判断是否合法即可。

时间复杂度：$O(2^n)$。

Code

// Problem: CF550B Preparing Olympiad
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/CF550B
// Memory Limit: 250 MB
// Time Limit: 2000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){int x=0,f=1;char ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;
ch=getchar();}while(ch>='0'&&ch<='9'){x=(x<<1)+
(x<<3)+(ch^48);ch=getchar();}return x*f;}
//#define mo
//#define M
//#define M
int n, m, i, j, k; 
int a[20], l, r, kx, ans; 

void dfs(int x, int sum, int mn, int mx)
{
	if(x>n)
	{
		if(sum>=l&&sum<=r)
			if(mx-mn>=kx) ++ans; 
		return ; 
	}
	dfs(x+1, sum, mn, mx); 
	dfs(x+1, sum+a[x], min(mn, a[x]), max(mx, a[x])); 
}

signed main()
{
//	freopen("tiaoshi.in","r",stdin);
//	freopen("tiaoshi.out","w",stdout);
	n=read(); l=read(); r=read(); kx=read(); 
	for(i=1; i<=n; ++i) a[i]=read(); 
	dfs(1, 0, 1000001, 0); 
	printf("%lld", ans); 
	return 0;
}