More than 2019 cattle off summer school camp (ninth field) -D Knapsack Cryptosystem (binary search)

Topic link: https: //ac.nowcoder.com/acm/contest/889/D

Meaning of the questions: simple meaning of the questions, from size 36 to a number of elements of the collection and is selected so that their sum.

Ideas: first impression with the search, complexity is 2 ^ 36, need to be optimized, just use binary search. That is half of the previous enumeration, and find whether there is a half ago after record and map enumeration and a half just to meet both for the sum.

AC Code:

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<string>
#include<map>
using namespace std;

typedef long long LL;
int n;
LL sum,a[40];
map<LL,string> mp;

int main(){
    scanf("%d%lld",&n,&sum);
    for(int i=0;i<n;++i)
        scanf("%lld",&a[i]);
    for(int i=0;i<(1<<n/2);++i){
        string s;
        LL tmp=0;
        for(int j=0;j<n/2;++j)
            if((i>>j)&1){
                tmp+=a[j];
                s+='1';
            }
            else{
                s+='0';
            }
        mp[tmp]=s;
    }
    for(int i=0;i<(1<<(n-n/2));++i){
        string s;
        LL tmp=0;
        for(int j=0;j<n-n/2;++j)
            if((i>>j)&1){
                tmp+=a[n/2+j];
                s+='1';
            }
            else{
                s+='0';
            }
        if(mp.count(sum-tmp)){
            cout<<mp[sum-tmp]<<s<<"\n";
            break;
        }
    }
    return 0;
}