Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	var n int
	fmt.Scan(&n)

	var sc = bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	ps := make([]int, n)
	for i := range ps {
		sc.Scan()
		p, _ := strconv.Atoi(sc.Text())
		ps[i] = p
	}

	mp := make([]int, n+1)
	ans := make([]byte, 0)
	var pp, max int
	for _, p := range ps {
		mp[p] = 1
		if p < pp {
			if mp[p+1] != 1 {
				fmt.Println(":(")
				return
			}
			ans = append(ans, ')')
		} else {
			for i := max; i < p-1; i++ {
				ans = append(ans, '(')
			}
			ans = append(ans, '(')
			ans = append(ans, ')')
		}
		if p > max {
			max = p
		}
		pp = p
	}
	fmt.Println(string(ans))
}

C++: #include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<(int)(n);i++)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
template<typename T,typename U> inline void chmax(T &x,U y){ if(y>x) x = y; }
template<typename T,typename U> inline void chmin(T &x,U y){ if(y<x) x = y; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/


struct RSQ{
    public:
        int n;
        vector<int> data;
        RSQ(int n_){
            n = 1;
            while(n<n_) n*=2;
            data.resize(2*n-1);
            for(int i=0;i<2*n-1;i++) data[i]=0;
        }
        void update(int k,int a){
            k+=n-1;
            data[k]=a;
            while(k>0){
                k=(k-1)/2;
                data[k]=data[k*2+1]+data[k*2+2];
            }
        }
        int query(int a,int b,int k,int l,int r){
            if(r<=a or b<=l) return 0;
            if(a<=l and r<=b) return data[k];
            else return query(a,b,k*2+1,l,(l+r)/2)+query(a,b,k*2+2,(l+r)/2,r);
        }
        int query(int a,int b){ return query(a,b,0,0,n); }
};

int main(){
    int n; cin >> n;
    vector<int> a(n);
    rep(i,n){
        cin >> a[i];
        //p[i]--;
    }

    string ans;
    int sum = 0;
    rep(i,n){
        if(i==0){
            sum += a[0];
            ans = string(a[0],'(');
            ans.push_back(')');
        }else{
            if(sum >= a[i]){
                ans.push_back(')');
            }
            else{
                int d = a[i] - sum;
                ans += string(d,'(');
                sum += d;
                ans.push_back(')');
            }
        }
    }
    RSQ seg(2*n);
    for(int i=0;i<ans.size();i++){
        if(ans[i] == '('){
            seg.update(i,1);
        }else{
            seg.update(i,-1);
        }
    }

    unordered_map<int,int> op,cl;
    int cli = 0;
    int opi = 0;
    for(int i=0;i<ans.size();i++){
        if(ans[i] == '('){
            op[++opi]=i;
        }else{
            cl[++cli]=i;
        }
    }

    for(int i=0;i<n;i++){
        int si = op[a[i]];
        int ei = cl[i+1];
        int num = seg.query(si+1,ei);
        if(num != 0){
            cout << ":(" << endl;
            return 0;
        }
    }



    //debug(ans);
    int cnt = 0;
    for(int i=0;i<ans.size();i++){
        if(ans[i] == '('){
            cnt++;
        }else{
            cnt--;
            if(cnt < 0){
                cout << ":(" << endl;
                return 0;
            }
        }
    }
    if(cnt != 0){
        cout << ":(" << endl;
        return 0;
    }
    cout << ans << endl;
}

C++: #include <iostream>
#include <stack>
using namespace std;
string s = "";
int n, p;

main()
{
    cin >> n;
    int c = 1;
    stack<int> st;
    for (int i = 0; i < n; i++)
    {
        cin >> p;
        while (c <= p)
        {
            st.push(c);
            s += '(';
            c++;
        }
        if (!st.empty() && st.top() == p)
        {
            s += ')';
            st.pop();
        }
        else
        {
            cout << ":(" << endl;
            return 0;
        }
    }
    cout << s << endl;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _SILENCE_ALL_CXX17_DEPRECATION_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include <map>
#include <fstream>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <assert.h>
#include <complex>
using namespace std;
#define LONG_INF 10000000000000
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007
#define MOD 998244353LL
#define seg_size 65536*4
#define REP(i,n) for(long long i = 0;i < n;++i)
int main() {
	string s;
	int n;
	cin >> n;
	vector<int> a;
	REP(i, n) {
		int tmp;
		cin >> tmp;
		a.push_back(tmp);
	}
	reverse(a.begin(), a.end());
	stack<int> now;
	int now_itr = n;
	for (int i = 0; i < n; ++i) {
		s.push_back('(');
		now.push(a[i]);
		while (now.empty() == false && now.top() == now_itr) {
			now_itr--;
			now.pop();
			s.push_back(')');
		}
	}
	if (now_itr != 0) {
		cout << ":(" << endl;
		return 0;
	}
	reverse(s.begin(), s.end());
	REP(i, s.length()) {
		if (s[i] == '(') s[i] = ')';
		else s[i] = '(';
	}
	cout << s << endl;
	return 0;
}