HDU 4671 Partition(定理题)

题目链接

这题，明显考察搜索能力。。。在中文版的维基百科中找到了公式。

#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
using namespace std;
#define MOD 1000000007
#define LL __int64
LL dp[200001];
int que[1001],flag[1001];
int main()
{
    int i,n,t,j,num;
    LL x;
    num = 0;
    for(i = 0;;i ++)
    {
        t = (3*i*i - i)/2;
        if(t > 300000) break;
        flag[num] = i;
        que[num++] = t;
        t = (3*i*i + i)/2;
        flag[num] = i;
        que[num++] = t;
    }
    dp[1] = 1;dp[2] = 2;
    dp[0] = 1;
    for(i = 3;i <= 100000;i ++)
    {
        for(j = 1;j <= 895;j ++)
        {
            if(que[j] > i)
            break;
            else
            x = dp[i-que[j]];
            if(flag[j]%2 == 1)
            {
                dp[i] = (dp[i] + x)%MOD;
            }
            else
            {
                dp[i] = (dp[i] - x)%MOD;
                if(dp[i] < 0)
                dp[i] += MOD;
            }
        }
    }
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        printf("%I64d
",dp[n]);
    }
    return 0;
}