Educational Codeforces Round 32 E 折半枚举

#include<cstdio>
#include<vector>
#include<cstring>
#include<algorithm>
using namespace std;
typedef long long ll;

const int A = 1e2 + 10;
const int B = 1e6 + 10;
int n,m,ed,a[A];
vector<int> F,G;

void dfs(int id,int now){
if(id>ed){
if(ed == n) G.push_back(now);
else        F.push_back(now);
return;
}
dfs(id+1,now);
dfs(id+1,(now+a[id])%m);
}

int main(){
scanf("%d%d",&n,&m);
for(int i=1 ;i<=n ;i++){
scanf("%d",&a[i]);
a[i] %= m;
}

ed = n/2;dfs(1,0);
sort(F.begin(),F.end());
F.erase(unique(F.begin(),F.end()),F.end());
ed = n;dfs(n/2+1,0);
sort(G.begin(),G.end());
G.erase(unique(G.begin(),G.end()),G.end());

int ans = 0;
ed = F.size();
for(int i=0 ;i<ed ;i++){
int val = m-1 - F[i];

int l = 0,r = G.size()-1,res = -1;
while(l<=r){
int mid = (l+r)>>1;
if(G[mid] <= val){
res = mid;
l = mid + 1;
}
else r = mid - 1;
}
if(res == -1) ans = max(ans,F[i]);
else          ans = max(ans,F[i]+G[res]);
}
printf("%d\n",ans);
return 0;
}