Lưu ý: Các code mẫu dưới đây chỉ mang tính tham khảo và có thể không AC được bài tập này

Code mẫu của flashmt

#include <iostream>
#include <algorithm>
#include <utility>
using namespace std;

int n, a[24], p[13], ans;
pair <int,int> d[1000000], e[1000000];

int main()
{
    cin >> n;
    for (int i = 0; i < n; i++) cin >> a[i];

    p[0] = 1;
    for (int i = 1; i <= 12; i++) p[i] = p[i - 1] * 3;

    int n1 = n / 2, n2 = n - n1;
    for (int i = 0; i < p[n1]; i++)
    {
        int s1 = 0, s2 = 0, tmp = i;
        for (int j = 0; j < n1; j++)
        {
            if (tmp % 3 == 1) s1 += a[j];
            if (tmp % 3 == 2) s2 += a[j];
            tmp /= 3;
        }
        d[i] = make_pair(s1 - s2, - s1 - s2);
    }

    for (int i = 0; i < p[n2]; i++)
    {
        int s1 = 0, s2 = 0, tmp = i;
        for (int j = 0; j < n2; j++)
        {
            if (tmp % 3 == 1) s1 += a[n1 + j];
            if (tmp % 3 == 2) s2 += a[n1 + j];
            tmp /= 3;
        }
        e[i] = make_pair(s1 - s2, - s1 - s2);
    }

    sort(d, d + p[n1]);
    int m1 = 1;
    for (int i = 1; i < p[n1]; i++)
        if (d[i].first != d[m1 - 1].first)
            d[m1++] = d[i];

    sort(e, e + p[n2]);
    int m2 = 1;
    for (int i = 1; i < p[n2]; i++)
        if (e[i].first != e[m2 - 1].first)
            e[m2++] = e[i];

    for (int i = 0, j = 0; i < m1 && j < m2;)
    {
        if (d[i].first == e[j].first) ans = max(ans, - d[i++].second - e[j++].second);
        else
            if (d[i].first < e[j].first) i++;
            else j++;
    }

    cout << ans / 2 << endl;
}

Code mẫu của happyboy99x

#include<bits/stdc++.h>
using namespace std;

#define TR(v,i) for(__typeof((v).begin())i=(v).begin();i!=(v).end();++i)
const int N = 24, MAX = 531441;
int a[N], n;
pair<int, int> c1[MAX], c2[MAX];

void backtrack(int l, int r, pair<int, int> res[], int &c, int w1 = 0, int w2 = 0) {
    if(l == r) res[c++] = make_pair(w1 - w2, w1 + w2);
    else {
        backtrack(l+1, r, res, c, w1, w2);
        backtrack(l+1, r, res, c, w1 + a[l], w2);
        backtrack(l+1, r, res, c, w1, w2 + a[l]);
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin >> n; for(int i = 0; i < n; ++i) cin >> a[i];
    int n1 = 0, n2 = 0;
    backtrack(0, n/2, c1, n1); backtrack(n/2, n, c2, n2);
    sort(c1, c1+n1); sort(c2, c2+n2);
    int res = 0;
    for(int i = 0, j = n2-1; i < n1; ++i) {
        while(j > 0 && c1[i].first + c2[j].first > 0) --j;
        if(c1[i].first + c2[j].first == 0)
            res = max(res, c1[i].second + c2[j].second);
    }
    cout << res/2 << '\n';
    return 0;
}

Code mẫu của ladpro98

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#define ii pair<int,int>
const int N = 25;
using namespace std;

pair<int, int> f[555555];
int a[N], n, lim, d, res;

int BS(int key) {
    int l = 1, r = d, k, m;
    while (l<=r) {
        m = (l+r) >> 1;
        if (f[m].first <= key) {
            k = m; l = m+1;
        }
        else r = m-1;
    }
    return k;
}

void Gen(int i, int x, int y) {
    if (i>lim) {
        d++;
        f[d].first = x-y;
        f[d].second = x;
        return;
    }
    Gen(i+1, x, y);
    Gen(i+1, x+a[i], y);
    Gen(i+1, x, y+a[i]);
}

void Back(int i, int x, int y) {
    if (i>n) {
        int t = BS(y-x);
        if (f[t].first==(y-x))
        res = max(res, f[t].second+x);
        return;
    }
    Back(i+1, x, y);
    Back(i+1, x+a[i], y);
    Back(i+1, x, y+a[i]);
}

int main()
{
    //freopen("DGOLD.in1","r",stdin);
    scanf("%d\n", &n);
    for(int i=1;i<=n;i++) scanf("%d\n", &a[i]);
    lim = n/2;
    Gen(1,0,0);
    sort(f+1, f+d+1);
    Back(lim+1,0,0);
    printf("%d", res);
    return 0;
}

Code mẫu của RR

#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <map>
#include <vector>

#define FOR(i,a,b) for(int i=(a),_b=(b); i <= _b; ++i)
#define FORD(i,a,b) for(int i=(a),_b=(b); i >= _b; --i)
#define REP(i,a) for(int i=0,_a=(a); i < _a; ++i)
using namespace std;

int n, a[25], res;

struct HashTable {
    static const int HKEY = 1000003;
    vector< pair<int,int> > h[HKEY];

    inline int key(int s) const {
        int res = s % HKEY;
        if (res < 0) res += HKEY;
        return res;
    }

    void insert(int s, int val) {
        int k = key(s);
        REP(i,h[k].size())
        if (h[k][i].first == s) {
            h[k][i].second = max(h[k][i].second, val);
            return ;
        }
        h[k].push_back(make_pair(s, val));
    }

    int get(int s) {
        int k = key(s);
        REP(i,h[k].size()) {
            if (h[k][i].first == s)
                return h[k][i].second;
        }
        return -1000111000;
    }
} best;

void attempt1(int i, int r, int sum1, int sum2) {
    if (i > r) {
        best.insert(sum1 - sum2, sum1);
        return ;
    }

    attempt1(i+1, r, sum1, sum2);
    attempt1(i+1, r, sum1+a[i], sum2);
    attempt1(i+1, r, sum1, sum2+a[i]);
}

void attempt2(int i, int r, int sum1, int sum2) {
    if (i > r) {
        res = max(res, best.get(sum2-sum1) + sum1);
        return ;
    }

    attempt2(i+1, r, sum1, sum2);
    attempt2(i+1, r, sum1+a[i], sum2);
    attempt2(i+1, r, sum1, sum2+a[i]);
}

int main() {
    scanf("%d", &n); FOR(i,1,n) scanf("%d", &a[i]);
    int l1 = 1, r1 = n/2;
    int l2 = r1+1, r2 = n;

    attempt1(l1, r1, 0, 0);
    attempt2(l2, r2, 0, 0);
    cout << res << endl;
}

Code mẫu của hieult

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iomanip>
#include <iostream>
#include <algorithm>

#include <ctime>
#include <deque>
#include <bitset>
#include <cctype>
#include <utility>
#include <cassert>

using namespace std;

typedef long long ll;
typedef double ld;
typedef unsigned int ui;
typedef unsigned long long ull;

#define Rep(i,n) for(int i = 0; i < (n); ++i)
#define Repd(i,n) for(int i = (n)-1; i >= 0; --i)
#define For(i,a,b) for(int i = (a); i <= (b); ++i)
#define Ford(i,a,b) for(int i = (a); i >= (b); --i)
#define Fit(i,v) for(__typeof((v).begin()) i = (v).begin(); i != (v).end(); ++i)
//#define Fitd(i,v) for(__typeof((v).rbegin()) i = (v).rbegin(); i != (v).rend(); ++i)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define sz(a) ((int)(a).size())
#define all(a) (a).begin(), (a).end()
#define ms(a,x) memset(a, x, sizeof(a))

template<class F, class T> T convert(F a, int p = -1) { stringstream ss; if (p >= 0) ss << fixed << setprecision(p); ss << a; T r; ss >> r; return r; }
template<class T> T gcd(T a, T b) { T r; while (b != 0) { r = a % b; a = b; b = r; } return a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template<class T> T sqr(T x) { return x * x; }
template<class T> T cube(T x) { return x * x * x; }
template<class T> int getbit(T s, int i) { return (s >> i) & 1; }
template<class T> T onbit(T s, int i) { return s | (T(1) << i); }
template<class T> T offbit(T s, int i) { return s & (~(T(1) << i)); }
template<class T> int cntbit(T s) { return s == 0 ? 0 : cntbit(s >> 1) + (s & 1); }

const int bfsz = 1 << 16;
char bf[bfsz + 5];
int rsz = 0;
int ptr = 0;
char gc() {
    if (rsz <= 0) {
        ptr = 0;
        rsz = (int) fread(bf, 1, bfsz, stdin);
        if (rsz <= 0)
            return EOF;
    }
    --rsz;
    return bf[ptr++];
}
void ga(char &c) {
    c = EOF;
    while (!isalpha(c))
        c = gc();
}
int gs(char s[]) {
    int l = 0;
    char c = gc();
    while (isspace(c))
        c = gc();
    while (c != EOF && !isspace(c)) {
        s[l++] = c;
        c = gc();
    }
    s[l] = '\0';
    return l;
}
template<class T> bool gi(T &v) {
    v = 0;
    char c = gc();
    while (c != EOF && c != '-' && !isdigit(c))
        c = gc();
    if (c == EOF)
        return false;
    bool neg = c == '-';
    if (neg)
        c = gc();
    while (isdigit(c)) {
        v = v * 10 + c - '0';
        c = gc();
    }
    if (neg)
        v = -v;
    return true;
}

typedef pair<int, int> II;

const ld PI = acos(-1.0);
const ld eps = 1e-9;

const int dr[] = {0, +1, 0, -1};
const int dc[] = {+1, 0, -1, 0};

const int inf = (int)1e9 + 5;
const ll linf = (ll)1e16 + 5;
const ll mod = (ll)1e9 + 7;

int n, a[25], b[25], m, Ma[(1 << 13) + 5], Mb[(1 << 13) + 5];
vector<II> Vt, V;
vector<int> V1, V2;

bool comp(const II &P0,const II &P1){
    if(P0.fi == P1.fi) return P0.se > P1.se;
    return P0.fi < P1.fi;
}

int  main()
{
//  freopen("in.txt", "r", stdin);
    cin >> n;
    Rep(i, n) cin >> a[i];
    m = n - n / 2;
    n = n / 2;
    Rep(i, m) b[i] = a[n + i];
    int res = 0, mask2, T1, T2, T;

    Rep(mask, (1 << n)){
        Ma[mask] = 0;
        Rep(i, n) Ma[mask] += getbit(mask, i) * a[i];
    }

    Rep(mask, (1 << m)){
        Mb[mask] = 0;
        Rep(i, m) Mb[mask] += getbit(mask, i) * b[i];
    }

    Rep(mask, (1 << n)){
        for(int mask1 = mask; mask1 > 0; mask1 = mask & (mask1 - 1)){
            mask2 = mask ^ mask1;
            T1 = Ma[mask1]; T2 = Ma[mask2];
            if(T1 == T2) res = max(res, T1 + T2);
            T = abs(T1 - T2);
            Vt.pb(mp(T, T1 + T2));
        }
    }

    sort(all(Vt), comp);
    V.pb(Vt[0]);
    for(int i = 1; i < sz(Vt); i++){
        if(Vt[i].fi > Vt[i - 1].fi) V.pb(Vt[i]);
    }

    int size = sz(V), t;
    Rep(i, size){
        V1.pb(V[i].fi);
        V2.pb(V[i].se);
    }

    Rep(mask, (1 << m)){
        for(int mask1 = mask; mask1 > 0; mask1 = mask & (mask1 - 1)){
            mask2 = mask ^ mask1;
            T1 = Mb[mask1]; T2 = Mb[mask2];
            if(T1 == T2) res = max(res, T1 + T2);
            T = abs(T1 - T2);
            t = lower_bound(all(V1), T) - V1.begin();
            if(t < size && V1[t] == T){
                res = max(res, V2[t] + T1 + T2);
            }
        }
    }

    cout << res / 2 << endl;
//  cout << clock() << endl;
    return 0;
}