CodeForces 288C - Polo the Penguin and XOR operation

看着样例推算了一下...得出的一个方法..让每个数与其选择的数XOR后为全1并且1尽可能的多.....

如样例

0 1 2 3 4

XOR 0 2 1 4 3

-----------------------

0 3 3 7 7

Program:

#include<iostream>
#include<stack>
#include<queue>
#include<stdio.h>
#include<algorithm>
#include<string.h>
#include<cmath>
#define ll long long
#define oo 1000000007
#define MAXN 1000005
using namespace std; 
int n;
ll ans[MAXN];
int main()
{  
      int i;
      ll x,sum; 
      while (~scanf("%d",&n))
      {
             x=1;
             while (x<=n) x<<=1;
             x--;
             memset(ans,-1,sizeof(ans)); 
             for (i=n;i>=0;i--)
             { 
                   if (ans[i]!=-1) continue;
                   while ((x^i)>n || ans[x^i]!=-1) x>>=1;
                   ans[x^i]=i,ans[i]=x^i;
             } 
             sum=0;
             for (i=0;i<=n;i++) sum+=i^ans[i];
             printf("%I64d\n",sum);
             for (i=0;i<=n;i++) printf("%I64d ",ans[i]);
             printf("\n");
      }
      return 0;
}