HDU 5014 异或之和

http://acm.hust.edu.cn/vjudge/contest/122814#problem/H

这道题就是求异或之和

知识点： a^b = c 等价于 b^c =a 和 a^c = b

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <cctype>
#include <vector>
#include <iterator>
#include <set>
#include <map>
#include <sstream>
using namespace std;

#define mem(a,b) memset(a,b,sizeof(a))
#define pf printf
#define sf scanf
#define spf sprintf
#define pb push_back
#define debug printf("!
")
#define MAXN 100000 + 10
#define MAX(a,b) a>b?a:b
#define blank pf("
")
#define LL long long
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
#define pqueue priority_queue
#define INF 0x3f3f3f3f

int n,m;

int a[MAXN],b[MAXN];

int main()
{
    int i,j;
    while(~sf("%d",&n))
    {
        mem(a,0);
        mem(b,-1);
        long long sum = 0;
        for(i=0;i<=n;i++) sf("%d",&a[i]);
        for(i=n;i>=0;i--)
        {
            int s = i;
            if(b[i] == -1)
            {
                int cnt = 0;
                while(s)
                {
                    s>>=1;
                    cnt++;
                }
                int tmp = (1<<cnt) -1;
                b[i] = i^tmp;
                b[i^tmp] = i;
            }
        }
        //for(i=0;i<=n;i++) pf("%d ",b[i]);
        for(i=0;i<=n;i++) sum+= i^b[i];
        pf("%I64d
",sum);

        for(i=0;i<n;i++)
        {
            pf("%d ",b[a[i]]);
        }
        pf("%d
",b[a[n]]);

    }
    return 0;
}