hdu 5014(贪+位运算)

题意：给你n+1个数（0->n）,让你为这n+1个数在0->n中分别找一个数与其异或，求最后的最大值

思路：假设一个数5 （二进制1 0 1），则找的另一个数在5的0位上最好是1 , 1位上最好为0，使其异或后为1.

#include <cstdio>
#include <cstring>
#define mod 10000007
typedef long long ll;
int n;
int a[100005],num[100005];
int main()
{
    while(scanf("%d",&n) != EOF)
    {
        for(int i = 0; i <= n; i++)
            scanf("%d",&a[i]);
        memset(num,-1,sizeof(num));
        ll sum = 0;
        for(int i = n; i >= 0; i--)
        {
            if(num[i] != -1)
                continue;
            int an=0,tmp = 1,ant=1;
            while(tmp < i)
            {
                if( (tmp & i) == 0)
                {
                    an+=ant;
                }
                tmp<<=1;
                ant*= 2;
            }
            num[i] = an;
            num[an] = i;
            sum+=(i^an)*2;
        }
        printf("%I64d\n",sum);
        printf("%d",num[a[0]]);
        for(int i = 1; i <= n; i++)
            printf(" %d",num[a[i]]);
        printf("\n");
    }
    return 0;
}