Problem

Create a quick direction iterator, which iterates over all 4 directions, i.e., up down left and right, in. a 2d space.

In many problems we have to do some operation on all the neighboring elements. So in that scenario we might have to write them one by one in the code. Instead of it if we generate the difference programatically we can write the code more neatly and understandable manner.

Solution

• Encode the directions in 2 bit binary bitset. Hence directions can be iterated using int [0,4).
• Other is a clever trick I found in someone else’s code online. Here we exploit the way of writing the directions.
• i (iota) in a complex plane, is an up direction, taking it through the integral powers rotates it in the complex plane
• using internal implementation of complex numbers in c++. Written the function of exponentiation.

Code

https://ideone.com/CGUrP8

P.S.

8 directional trick: {0,-1,-1,0,1,-1,1,1,0}

Code

#include <iostream>
#include <vector>
using namespace std;
pair<int,int> dir(int d){
	d %= 4;
	return make_pair(d/2?d%2*2-1:0,d/2?0:d%2*2-1);
}
int main() {
	vector<string> v = {"left","right","up","down"};
	cout<<"i\tj"<<endl;
	for(int i=0; i<4; i++)
		cout<<dir(i).first<<'\t'<<dir(i).second<<"\td:"<<i<<'\t'<<v[i]<<endl;
	
	// second approach
	vector<int> dirs={0,1,0,-1,0};
	v = {"right","down","left","up"};
	cout<<endl<<"i\tj"<<endl;
	for(int i=0; i<4; i++)
		cout<<dirs[i]<<'\t'<<dirs[i+1]<<"\td:"<<i<<'\t'<<v[i]<<endl;
		
	return 0;
}

Ideone it!