poj2081

1．链接地址

 https://vjudge.net/problem/POJ-2081

2．问题描述

 The Recaman's sequence is defined by a0 = 0 ; for m > 0, a _m = a _m−1 − m if the rsulting a _m is positive and not already in the sequence, otherwise a _m = a _m−1 + m.
The first few numbers in the Recaman's Sequence is 0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11, 22, 10, 23, 9 ... 
Given k, your task is to calculate a _k.

输入样例

7
10000
-1

输出样例

20
18658

3．解题思路

 这一看就是打表题

4．算法实现源代码

#include<iostream>
#include<cstring>
#include<string>
#include<algorithm>
using namespace std;
const int maxn=500000+10;
int vis[5000005];
int a[maxn];

void init()
{
    memset(vis,0,sizeof(vis));
    memset(a,0,sizeof(a));
    a[0]=0;
    vis[0]=1;
    int flag=0;
    for(int i=1;i<maxn;i++)
    {
        flag=a[i-1]-i;
        if(flag>0&&vis[flag]==0)
        {
            a[i]=flag;
            vis[flag]=1;
        }
        else
        {
            a[i]=a[i-1]+i;
            vis[a[i]]=1;
        }
    }
}

int main()
{
    init();
    int n;
    while(scanf("%d",&n)&&n!=-1)
    {
        printf("%d\n",a[n]);
    }
}