URI: 2013 - No Máximo Duas Vezes

#include <iostream>

using namespace std;

int main()
{
    string number;
    cin >> number;

    int ocurr[10] = {0};
    int greater(9);

    string::iterator c = number.begin();
    int n = *c - '0';

    while (ocurr[n] < 2 && c != number.end())
    {
        ocurr[n]++;
        c++;
        n = *c - '0';
    }

    if (c != number.end())
    {
        while (n > 0 && ocurr[n] == 2)
        {
            (*c)--;
            n--;
        }

        while (n == 0 && ocurr[0] == 2 && c != number.begin())
        {
            do
            {
                c--;
                n = *c - '0';
                ocurr[n]--;
            }
            while (n == 0);

            do
            {
                (*c)--;
                n--;
            }
            while (n > 0 && ocurr[n] == 2);
        }

        if (c != number.begin())
            ocurr[*c - '0']++;

        for (c++; c != number.end(); c++)
        {
            while (ocurr[greater] == 2)
                greater--;

            *c = greater + '0';
            ocurr[greater]++;
        }
    }

    const char* str = number.c_str();
    cout << (str[0] == '0' ? str + 1 : str) << endl;

    return 0;
}