help with shifting elelemnts in arrays

[zerocool1822]

hello , ive been at this for 2 days now and i just cant get it. im trying to figure out how to shift The columns of a table one position to the left im at the point of giving up but i thought id atleast try to get some help online. my method is below. as u can see , its a mess , as ive been trying to tinker with it and get it to shift the right direction , but its not happening.

public static void shiftRight(int[][] table){	
		for(int i = table.length-1; i > 0; i--){
			table[0]=table[i-1];		
		}
		table[0]=table[table.length-1];
		
	}

[JosAH]

First we have to agree on a few things: columns run from left to right and rows run from top to bottom, right? A table element (row, col) is stored in a two dimensional array[row][col], right? If a bunch of columns is moved to the left, what happens to the column at the far right? What happens to the column that is 'shifted away'?

kind regards,

Jos

[zerocool1822]

ok , yes i agree with what you said and understand that. the column at the far right moves over 1 to the left. and the column thats shifted away moves over 1 to the left as well , so its like they rotate to the left as they get shifted.

[JosAH]

ok , yes i agree with what you said and understand that. the column at the far right moves over 1 to the left. and the column thats shifted away moves over 1 to the left as well , so its like they rotate to the left as they get shifted.

Ah, ok, so you want to rotate all columns one position, e.g. A B C D E --> B C D E A, correct?

kind regards,

Jos

[zerocool1822]

yes so like
9 3 0 9 8
7 1 5 6 3
0 8 0 6 8
1 6 8 7 5
3 0 4 4 8

shifted to the left would be
3 0 9 8 9
1 5 6 3 7
8 0 6 8 0
6 8 7 5 1
0 4 4 8 3

[JosAH]

Yep, that's rotating to the left alright; for each element i in an array, you want to plug a value in and take a value out of it (to be plugged in somewhere else):

takeout= array[i];
array[i]= plugin;
plugin= takeout;

For the rightmost element you want to plug in the leftmost element, i.e. array[0], so your code becomes:

plugin= array[0];
for (int i= array.length-1; i >= 0; i--) {
   takeout= array[i];
   array[i]= plugin;
   plugin= takeout;
}

This code rotates a single one dimensional array; a table is just an array of one dimensional arrays, so you have to perform the above code on every row of your table ...

kind regards,

Jos

[zerocool1822]

when u say take out , you mean extracting an elements from the column right? so its like , take out an element from table[i]

[JosAH]

when u say take out , you mean extracting an elements from the column right? so its like , take out an element from table[i]

Yup, just before you plug in a new element at a position in the array, you have to take out the previous value (to plug it in at another position). Follow the code step by step for a small example array (say, three elements) and see how it works.

kind regards,

Jos

[zerocool1822]

this is what i came up with, it works in theory lol, i was using modulus to extract the numbers. but ofcourse it doenst perform right when i run it

public static void shiftRight(int[][] table){
		
		for (int i= table.length-1; i >= 0; i--) {
			table[(i+1)%table[i].length]=table[i];
			table[i]=table[0];
			table[0]=table[(i+1)%table[i].length];
			
			
		
		
		}
		}

[JosAH]

Sorry to say so, but it doesn't work in my theory; try it with a small table (two dimensional array) and see for yourself ...

kind regards,

Jos