C - Recaman's Sequence

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Time Limit:3000MS     Memory Limit:60000KB     64bit IO Format:%I64d & %I64u

Submit Status​ ​Practice​ ​POJ 2081

System Crawler (2016-05-11)

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

打表输出即可。

#include <stdio.h>
#include <string.h>
bool vis[6555550];
int result[500000+5];
int main()
{
  memset(vis,false,sizeof(vis));
  result[0]=0;vis[0]=true;
  for(int i=1;i<=500000;i++)
  {
    int x=result[i-1]-i;
    if(x>0&&!vis[x])
    {
      result[i]=x;
      vis[x]=true;
    }
    else
    {
      result[i]=result[i-1]+i;
      vis[result[i]]=true;
    }
  }
  int n;
  while(~scanf("%d",&n)&&n!=-1)
  {
    printf("%d\n",result[n]);
  }
  return 0;
}