EdgeSolver with templates

main.cpp

#include <iostream>
#include <vector>
#include <string>
#include <array>
#include <fstream>

using std::cout;
using std::endl;

typedef std::vector<std::array<char, 4>> Board;

void fastswap(Board::iterator it1, Board::iterator it2){
    std::swap(*(int*)it1->data(), *(int*)it2->data());
}

void fastrot(Board::iterator it) {
    static_assert(sizeof(int) == 4, "rotation will not work");
    int &val = *(int*)it->data();
    val = (val << 8) | (val >> ((sizeof(int) * 8 - 8)));
}

template<int size>
bool checkLeftEdge(Board::iterator begin, Board::iterator right){
    if ((right - begin) % size == 0)
        return true;
    auto left = right - 1;
    char c1 = (*right)[3], c2 = (*left)[1];
    return c1 - 32 == c2 || c1 == c2 - 32;
}

template<int size>
bool checkTopEdge(Board::iterator begin, Board::iterator bottom){
    if (bottom < begin + size)
        return true;
    auto top = bottom - size;
    char c1 = (*bottom)[0], c2 = (*top)[2];
    return c1 - 32 == c2 || c1 == c2 - 32;
}

template<int size>
inline bool isLastElementValid(Board::iterator begin, Board::iterator last){
    return
        checkTopEdge<size>(begin, last) &&
        checkLeftEdge<size>(begin, last);
}

template<int size>
bool recurse(Board::iterator begin, Board::iterator end, Board::iterator len){
    if (len == end)
        return true;
    for (auto it = len; it != end; ++it){
        fastswap(len, it);
        for (int j = 0; j < 4; ++j){
            if (isLastElementValid<size>(begin, len)){
                bool success = recurse<size>(begin, end, len + 1);
                if (success)
                    return true;
            }
            fastrot(len);
        }
        fastswap(len, it);
    }
    return false;
}

int to_index(int x, int y, int size){ return y * size + x; }

void draw(const Board &board, int size){
	for (int y = 0; y < size; ++y){
		cout << std::string(size * 4 + 1, '-') << endl;
		for (int x = 0; x < size; ++x)
			cout << "| " << board[to_index(x, y, size)][0] << " ";
		cout << "|" << endl;
		for (int x = 0; x < size; ++x)
			cout << "|" << board[to_index(x, y, size)][3] << " " << board[to_index(x, y, size)][1];
		cout << "|" << endl;
		for (int x = 0; x < size; ++x)
			cout << "| " << board[to_index(x, y, size)][2] << " ";
		cout << "|" << endl;
	}
	cout << std::string(size * 4 + 1, '-') << endl;
	cout << endl;
}

int main(){
	std::ifstream in ("in.txt");
	if (!in)
		return 1;

	int size;
	in >> size;
	Board board(size * size);
	for (auto& str : board){
		in.ignore();
		in.read(str.data(), 4);
	}

	bool success = false;
	if(size == 2) success = recurse<2>(board.begin(), board.end(), board.begin());
	else if(size == 3) success = recurse<3>(board.begin(), board.end(), board.begin());
	else if(size == 4) success = recurse<4>(board.begin(), board.end(), board.begin());
	else if(size == 5) success = recurse<5>(board.begin(), board.end(), board.begin());
	if (success)
		draw(board, size);

	std::cin.ignore();
	std::cin.get();
}