UVa10718 - Bit Mask（不错的贪心）

#include<cstdlib>
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<set>
#include<map>
#include<list>
#include<queue>
#include<vector>
#define LL long long
#define UI unsigned int
#define inf 0x7fffffff
#define eps 1e-7
#define M 105
#define N 1010
using namespace std;
UI m,n,t,u,l;
bool a[32];
bool b[32];
unsigned int tranxiao(bool a[])
{
    UI ans=0;
    for (int i=31;i>=0;--i )
    	ans=ans*2+a[i];
    	return ans;
}
unsigned int tranda(bool a[],int k)
{
    UI ans=0;
    for (int i=31;i>=k;--i )
    	ans=ans*2+a[i];
    while(k)
    {
        ans=ans*2+1;k--;
    }
    	return ans;
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("ex.in","r",stdin);
#endif
    int ncase=0;
//    scanf("%d",&t);
    while(scanf("%u%u%u",&n,&l,&u)==3)
    {
        memset(a,0,sizeof(a));
        memset(b,0,sizeof(b));
        t=n;
        for(int i=0;i<32&&t;i++)
        {
            b[i]=t%2;
            t/=2;
        }
        for(int i=31;i>=0;i--)//好的贪心
        {
            a[i]=1;
            if(tranxiao(a)>u)//当前可能最小值
            {
                a[i]=0;continue;
            }
            a[i]=0;
            if(tranda(a,i)<l)//当前可能最大值
            {
                a[i]=1;continue;
            }
            if(b[i]==1)a[i]=0;
            else a[i]=1;
        }
        printf("%u\n",tranxiao(a));
    }
    return 0;
}