Ordered Numbers en C++. Compile with g++ ordered.cpp -ansi -O3

ordered.cpp

#include <string>
#include <iostream>
#include <cstdlib>
#include <cstdio>

using namespace std;

	// O(d) where d is the length of input_N
int firstIndexOfUnorderedPair(const string &input_N) {

	for (int i = 0; i+1 < input_N.length(); i++) {
		if (input_N[i] > input_N[i+1]) {
			return i;
		}
	}
	return input_N.length();
}
	// O(d) where d is the length of input_N
long long getOrderedLowerBound(string &input_N) {
	
	int unordered_index = firstIndexOfUnorderedPair(input_N);
	
	if (unordered_index < input_N.length()) {
		int current_index = input_N.length()-1;
		input_N[unordered_index]--;

		while (current_index > unordered_index) {
			input_N[current_index--] = '9';
		}
		while (current_index > 0 && input_N[current_index-1] > input_N[current_index]) {
			input_N[current_index--] = '9';
			input_N[current_index]--;
		}
	}
	return atol(input_N.c_str());
}
	// O(d) where d is the length of input_N
void solveTest(int test) {

	string input_N;
	cin >> input_N;

	cout << "Caso " << test << ": N=" << input_N;
	long long ordered_N = getOrderedLowerBound(input_N);
	cout << ", O=" << ordered_N << "\n"; 
}
	// O(test_cases*max_d)
int main() {
		// redirect standard streams
	freopen("entrada.txt", "r", stdin);
	freopen("salida.txt", "w", stdout);
		// unbind iostream from stdio
	ios_base::sync_with_stdio(0);
	cout.tie(0);
	cin.tie(0);

	int test_cases;
	cin >> test_cases;
	
	for (int test = 1; test <= test_cases; test++) {
		solveTest(test);
	}
	return 0;
}