poj 1579 Moving Tables（水）

Description

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.

Input

The input consists of several test cases. Each line of the input contains an integer k where 0 <= k <= 500000. 
The last line contains an integer −1, which should not be processed.

Output

For each k given in the input, print one line containing a _k to the output.

Sample Input

7
10000
-1

Sample Output

20
18658
题意：找第k个Recaman's sequence数。
注意：没什么好注意的。
ac代码：

#include<stdio.h>
int d[600000],vis[9000000];
int main()
{
    int a,b,i,j,n;
    d[0]=0;
    for(i=0;i<500005;i++)
    {
        if(d[i-1]-i<0||vis[d[i-1]-i]==1)
        d[i]=d[i-1]+i;
        else if(!vis[d[i-1]-i])
        d[i]=d[i-1]-i;
        vis[d[i]]=1;
    }
    while(scanf("%d",&n))
    {
        if(n==-1)
        break;
        printf("%d\n",d[n]);
    }
}