Lagrange Snail Matrix Generator - http://enghqii.tistory.com/24

LSMG.cpp

#include <iostream>
#include <sstream>
using namespace std;

typedef int uint;

std::string LagrangeGenerator(const uint k){

	uint** arr = new uint*[k];
	for(uint i=0;i<k;i++){ arr[i] = new uint[k]; }

	for(uint i=0;i<k;i++){
		for(uint j=0;j<k;j++){
			arr[i][j] = 0;
		}
	}

	// 달팽이 배열 만들기.

	uint i=0, j=0;
	uint n = 1;
	uint dir = 0; // 0 to 3
	
	arr[i][j] = n++;

	auto dircng = [](uint dir){ 
		dir++; 
		dir%=4; 
		return dir; 
	};

	while(true){
		
		switch(dir){
		case 0:
			if(j+1 >= k || arr[i][j+1] != 0){ dir = dircng(dir); continue; }
			j += 1;
			break;
		case 1:
			if(i+1 >= k || arr[i+1][j] != 0){ dir = dircng(dir); continue; }
			i += 1;
			break;
		case 2:
			if(j-1 >= k || arr[i][j-1] != 0){ dir = dircng(dir); continue; }
			j -= 1;
			break;
		case 3:
			if(i-1 >= k || arr[i-1][j] != 0){ dir = dircng(dir); continue; }
			i -= 1;
			break;
		}

		arr[i][j] = n++;
		if(n-1 >= k*k) 
			break;
	}
	
	/*
	for(int i=0;i<k;i++){
		for(int j=0;j<k;j++){
			cout<<arr[i][j]<<'\t';
		}
		cout<<endl;
	}
	*/

	// 만듬.

	std::ostringstream ret;

	ret<<"=1.0*";
	
	for(uint j=0; j < k * k; j++){

		uint y = arr[j/k][j%k];
		double factor = 1;

		for(uint f = 0; f < k*k; f++){
			if(j != f){
				ret << "(x-" << f << ")";
				ret << "/"<<j-f<<"*";
			}
		}
		ret<<y;
		ret<<"+";
	}
	
	ret<<"0;";

	for(uint i=0;i<k;i++){ delete [] arr[i]; }
	delete[] arr;

	return ret.str();
}

int main(int argc,char** argv){
	
	if(argc < 2){
		cout<<"no argument specified."<<endl;
		return 0;
	}

	try{
		int k = std::stoi(argv[1]);

		if(k <= 0){
			cout<<"argument out of range"<<endl;
			return 0;
		}

		cout<<LagrangeGenerator(k).c_str()<<endl;

	}catch(std::exception const & e){
		cout<<"error : " << e.what() <<endl;
	}
}