Description
Farmer John commanded his cows to search for different sets of numbers that sum to a given number. The cows use only numbers that are an integer power of 2. Here are the possible sets of numbers that sum to 7: 1) 1+1+1+1+1+1+1 2) 1+1+1+1+1+2 3) 1+1+1+2+2 4) 1+1+1+4 5) 1+2+2+2 6) 1+2+4 Help FJ count all possible representations for a given integer N (1 <= N <= 1,000,000).
给出一个N(1≤N≤10^6),使用一些2的若干次幂的数相加来求之.问有多少种方法
Input
一个整数N.
Output
方法数.这个数可能很大,请输出其在十进制下的最后9位.
Sample Input
7
Sample Output
6
HINT
- 1+1+1+1+1+1+1
- 1+1+1+1+1+2
- 1+1+1+2+2
- 1+1+1+4
- 1+2+2+2
- 1+2+4
考虑到n不大,所以我们可以直接用完全背包,复杂度应该是(O(nln n))级别
其实发现奇数只能通过偶数+1得到,而偶数可以通过奇数+1,也可以通过其折半的偶数翻倍得来,因此得到方程
[f[i]=egin{cases} f[i-1]&,i\%2=1\ f[i-1]+f[i/2]&,i\%2=0end{cases}
]
复杂度(O(n))
/*program from Wolfycz*/
#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define inf 0x7f7f7f7f
using namespace std;
typedef long long ll;
typedef unsigned int ui;
typedef unsigned long long ull;
inline char gc(){
static char buf[1000000],*p1=buf,*p2=buf;
return p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++;
}
inline int frd(){
int x=0,f=1;char ch=gc();
for (;ch<'0'||ch>'9';ch=gc()) if (ch=='-') f=-1;
for (;ch>='0'&&ch<='9';ch=gc()) x=(x<<1)+(x<<3)+ch-'0';
return x*f;
}
inline int read(){
int x=0,f=1;char ch=getchar();
for (;ch<'0'||ch>'9';ch=getchar()) if (ch=='-') f=-1;
for (;ch>='0'&&ch<='9';ch=getchar()) x=(x<<1)+(x<<3)+ch-'0';
return x*f;
}
inline void print(int x){
if (x<0) putchar('-'),x=-x;
if (x>9) print(x/10);
putchar(x%10+'0');
}
const int N=1e6,p=1e9;
int f[N+10];
int main(){
int n=frd(); f[0]=1;
for (register int i=1;i<=n;i+=2) f[i]=f[i-1],f[i+1]=(f[i]+f[(i+1)>>1])%p;
printf("%d
",f[n]);
return 0;
}