Simulation of metal piece rusting

rust.cpp

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <unordered_set>

static const int dim = 10;

std::string readLine(std::istream& in) {
	std::string str;
	std::getline(in, str);
	return str;
}

class Metal final {
public:
	void fill(std::istream& in) {
		for (size_t i = 0; i < dim * dim; i++) {
			char c;
			in >> c;
			if (c == '\n') continue;
			cells[i / dim][i % dim] = c;
		}
	}

	void rust() {
		for (size_t i = 0; i < dim; i++) {
			for (size_t j = 0; j < dim; j++) {
				char c = cells[i][j];
				if (c == rustParticle) {
					// Spread up
					if (i > 0) {
						cells[i - 1][j] != rustresist && cells[i - 1][j] != rustParticle ? cells[i - 1][j] = rustCreepsIn : 0;
					}
					// Spread right
					if (j < dim - 1) {
						cells[i][j + 1] != rustresist && cells[i][j + 1] != rustParticle ? cells[i][j + 1] = rustCreepsIn : 0;
					}
					// spread down
					if (i < dim - 1) {
						cells[i + 1][j] != rustresist && cells[i + 1][j] != rustParticle ? cells[i + 1][j] = rustCreepsIn : 0;
					}
					if (j > 0) {
						cells[i][j - 1] != rustresist && cells[i][j - 1] != rustParticle ? cells[i][j - 1] = rustCreepsIn : 0;
					}
				}
			}
		}

		for (size_t i = 0; i < dim; i++) {
			for (size_t j = 0; j < dim; j++) {
				if (cells[i][j] == rustCreepsIn) {
					cells[i][j] = rustParticle;
				}
			}
		}
	}

	void print(std::ostream& out) const {
		for (size_t i = 0; i < dim; i++) {
			for (size_t j = 0; j < dim; j++) {
				out << cells[i][j];
			}
			out << '\n';
		}
	}
private:
	const char rustParticle = '!';
	const char rustresist = '#';
	const char rustCreepsIn = '%';
	char cells[dim][dim];
};

int main()
{
	Metal m;
	m.fill(std::cin);
	int n = 0;
	std::cin >> n;

	for (size_t i = 0; i < n; i++) {
		m.rust();
	}
	m.print(std::cout);
}