TYVJ1340 送礼物

 1 #include <iostream>
 2 #include <cstdlib>
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <algorithm>
 6 #define min(a, b) ((a) < (b) ? (a) : (b))
 7 #define max(a, b) ((a) > (b) ? (a) : (b)) 
 8 
 9 inline void read(long long &x)
10 {
11     x = 0;char ch = getchar(), c = ch;
12     while(ch < ‘0‘|| ch > ‘9‘)c = ch, ch = getchar();
13     while(ch <= ‘9‘ && ch >= ‘0‘)x = x * 10 + ch - ‘0‘, ch = getchar();
14     if(c == ‘-‘)x = -x; 
15 }
16 
17 const int MAXN = 45 + 10;
18 
19 long long W,n,g[MAXN],num1[(1 << 23) + 100],num2[(1 << 23) + 100],cnt1,cnt2,ans,mid;
20 
21 void dfs1(long long step, long long now)
22 {
23     if(now > W)return;
24     if(step > mid)
25     {
26         if(now)num1[++cnt1] = now;
27         return;
28     }
29     dfs1(step + 1, now + g[step]);
30     dfs1(step + 1, now);
31 }
32 
33 void dfs2(long long step, long long now)
34 {
35     if(now > W)return;
36     if(step > n)
37     {
38         if(now)num2[++cnt2] = now;
39         return;
40     }
41     dfs2(step + 1, now + g[step]);
42     dfs2(step + 1, now);
43 }
44 
45 int main()
46 {
47     read(W), read(n);
48     mid = n/2;
49     for(register long long i = 1;i <= n;++ i)
50         read(g[i]);
51     dfs1(1, 0);
52     std::sort(num1 + 1, num1 + 1 + cnt1);
53     dfs2(mid + 1, 0);
54     std::sort(num2 + 1, num2 + 1 + cnt2);
55     ans = max(num1[cnt1], num2[cnt2]);
56     long long l = 1;
57     for(register long long i = cnt2;i >= 1;-- i)
58     {
59         while(num2[i] + num1[l] <= W && l <= cnt1)++ l;
60         -- l;
61         ans = max(ans, num2[i] + num1[l]);
62     }
63     printf("%lld", ans);
64     return 0;
65 }