H - Sumsets POJ 2229

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). 

Input

A single line with a single integer, N.

Output

The number of ways to represent N as the indicated sum. Due to the potential huge size of this number, print only last 9 digits (in base 10 representation).

Sample Input

7

Sample Output

6

当i为奇数的时候a[i]=a[i-1]

当i为偶数的时候a[i]=a[i-1]+a[i/2]

#include<stdio.h>
int a[1000100];
int main()
{
	int i,n;
	a[1]=1;a[2]=2;
	for(i=3;i<1000100;i++)
	{
		if(i&1)
		{
			a[i]=a[i-1]%1000000000;
		}
		else a[i]=(a[i/2]+a[i-2])%1000000000;
	}
	while(scanf("%d",&n)!=EOF)
	{
		printf("%d\n",a[n]);
	}
}