Sumsets——hdu2709

Problem 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

搜索的话会超时，直接打表找规律得

偶数时a[ i ]=(a[ i-1 ]+a[ i/2 ])(记得mod)

奇数时等于前一偶数的

#include <iostream>
using namespace std;
__int64 a[1000001];
int main()
{
 int i,n;
 a[1]=1;
 a[2]=2;
 for(i=3;i<1000001;i++){
  	if(i&1) 
  		a[i]=a[i-1];//因为加1后并为能形成2得幂次数 
  	else 
	  	a[i]=(a[i-2]+a[i/2])%1000000000;
 }
 while(cin>>n) 
 	cout<<a[n]<<endl;
 return 0;
}