hihocoder 1754

题目链接： https://hihocoder.com/problemset/solution/1327177

解题思路：

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 
 4 typedef long long LL;
 5 const int MAXN = 100005;
 6 const LL MOD7 = 1e9+7;
 7 
 8 LL C;
 9 int n;
10 int a[64];
11 int cnt[64];
12 
13 map<LL,int> ind2;
14 map<int,LL> pow2;
15 
16 void init()
17 {
18     pow2[0] = 1;
19     ind2[1] = 0;
20     for (int i=1;i<63;++i)
21     {
22         pow2[i] = pow2[i-1]*2;
23         ind2[pow2[i]]=i;
24     }
25 }
26 
27 void work()
28 {
29     cnt[0]=a[0];
30     for (int i=1;i<63;++i)
31     {
32         cnt[i]=cnt[i-1]+a[i];
33     }
34     LL tmp=C;
35     LL ans = 0LL;
36     for (int i=62;i>=0;--i)
37     {
38         if (tmp>=pow2[i])
39         {
40             if (a[i]==1) {
41                 if (cnt[i]>=1) ans += pow2[cnt[i]-1];
42             } else {
43                 ans += pow2[cnt[i]] - 1;
44                 break;
45             }
46             tmp-=pow2[i];
47         }
48     }
49     printf("%lld\n",ans);
50 }
51 
52 int main()
53 {
54     init();
55 #ifndef ONLINE_JUDGE
56     freopen("test.txt","r",stdin);
57 #endif // ONLINE_JUDGE
58     while ( scanf("%d%lld",&n,&C)!=-1 ) {
59     LL d;
60     for (int i=1;i<=n;++i)
61     {
62         scanf("%lld",&d);
63         a[ind2[d]]=1;
64     }
65     work();
66     }
67     return 0;
68 }