Решение задачи Скобки(3) с Меньшиков

#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
 
using namespace std;
const int MAX_VALUE = 1e9;
int n;
string str;
vector<vector<int> > mas;
void input()
{
    cin>>str;
    n = str.size();
    mas = vector<vector<int> >(n,vector<int>(n,0));
}
string open = "([";
string clos = ")]";
bool isPair(char f, char s)
{
    int posF = open.find(f);
    int posS = clos.find(s);
    return posF == posS && posF != -1;
}
string Pair(char one)
{
    int pos = open.find(one);
    if (pos == -1)
        pos = clos.find(one);
   
    return string(&open[pos],1) + string(&clos[pos],1);
}
string getAnswer(int l, int r)
{
    if (l > r) return "";
    if (l == r)
        return Pair(str[l]);
    int border = (isPair(str[l],str[r]) ? mas[l+1][r-1] : MAX_VALUE);
    if (border == mas[l][r])
        return str[l] + getAnswer(l+1,r-1) + str[r];
    for (int m = l; m < r; m++)
    {
        if (mas[l][m] + mas[m+1][r] == mas[l][r])
            return getAnswer(l,m) + getAnswer(m+1,r);
    }
}
void solve()
{
    for (int i=0;i<n;i++)
        mas[i][i] = 1;
    for (int len = 1; len < n; len++) {
        for (int i=0;i<n;i++) {
            int j = i + len;
            if (j>=n) break;
 
            int curLen = MAX_VALUE;
            if (isPair(str[i],str[j]))
                curLen = mas[i+1][j-1];
            for (int m = i; m < j; m++)
                curLen = min(curLen, mas[i][m] + mas[m+1][j]);
            mas[i][j] = curLen;
        }
    }
 
    string answer = "";
    answer = getAnswer(0,n-1);
    cout<<answer;
}
int main()
{
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
 
    input();
    solve();
    return 0;
}