Jumping to function start from within certain code part - c++

Question

include <iostream>
using namespace std;
int Solution(int i_start, int j_start, int i_end, int j_end, int s)
{
int row_dif=i_start-i_end;
int col_dif=j_start-j_end;
while (col_dif !=0 )
{
row_dif=i_start-i_end;
col_dif=j_start-j_end;
if ((row_dif>0) && (col_dif>0))
{
i_start=i_start-2;
j_start--;
}
if ((row_dif>0)) && (col_dif<0)
{
i_start=i_start-2;
j_start++;
}
if ((row_dif<0) && (col_dif>0 ))
{
i_start=i_start+2;
j_start--;
}
if ((row_dif<0) && (col_dif<0))
{
i_start=i_start+2;
j_start++;
}
if (row_dif=0)
{
if (col_dif>0)
{
j_start-2;
}
else if (col_dif<0)
{
j_start+2;
}
else //row_dif=0 dhe col_dif=0
{
cout<<"Problem solved "<<endl;
}
}
}
// col_dif=0
if (row_dif<=-4)
{
i_start=i_start+2;
j_start++;
}
if (row_dif>=4)
{
i_start=i_start-2;
j_start--;
}
}
I am trying to solve Red Knight shortest path with my own method but I am stuck at a part where I need to jump to function start. as an entry-condition I have decided to use row_dif=0 but when row_dif does reach 0 value, I also need to check if there could be more moves (row_dif>=4 or row_dif<=-4) available. And if there are available moves I need to jump to while loop again.

Answer 1

I am stuck at a part where I need to jump to function start
It seems to me like you are stumbling onto the idea of a recursive function. Something along the lines of
return Solution(i_start - 2, j_start - 1, i_end, j_end, s + 1)
Recursion causes the state to be pushed onto the program stack. This idea of a stack is important.
The Red Knight Shortest Path challenge looks to me an awful lot pathfinding. Specifically, A* pathfinding with constrained movements.
The recursive approach uses a stack and is depth-first. For a solution where you want to minimize moves, you want to use a breadth-first approach. You will still wind up using a stack, but your primary structure will be a queue.
As this challenge seems to be geared towards search algorithms, I would suggest studying up on everything I mentioned.

Answer 2

You should write a function int sign( int i ) that returns -1, 0 or +1 for integer less than, equal to or bigger than zero. Then all of your code becomes:
if( row_dif == 0 && col_dif == 0 ) {
// done interrupt
}
i_start -= 2 * sign( row_dif );
j_start -= 1 * sign( col_dif );
plus this code handles situation when col_dif is equal to 0, but row_dif is not, which you did not in your code.
To add your condition change your loop to:
while( true ) {
row_dif=i_start-i_end;
col_dif=j_start-j_end;
if( col_dif == 0 ) {
if( row_dif == 0 ) {
// done
break;
}
if( std::abs( row_dif ) < 4 )
break; // does not look right but follows your logic
col_dif = sign( row_dif );
}
i_start -= 2 * sign( row_dif );
j_start -= 1 * sign( col_dif );
}
Note: comparation operator in C++ is == not = and this is common mistake for novice C++ programmers.