Question

Doing recursion to match digits of two inputted integers. Found this online and it works but I wanna understand how each line works. Like why x %10 == y%10 and calling DigitMatch(x/10,y/10)?

public int digitMatch(int x, int y){

    if(x < 0 || y < 0){

      throw new IllegalArgumentException();

    }

      else if(x < 10 || y < 10){

         if(x % 10 == y % 10)

            return 1;

         else

             return 0;

      } else if( x % 10 == y % 10){

         return 1 + digitMatch(x/10, y/10);

      }

    else{

         return digitMatch(x/10,y/10);

    }

Answer 1

this program number of digits of two inputted int x and y matches .
this program starts with left most digit of in x and y.
and keep traversing right(digit by digit) in each recursive call.
if in any recursive call it found unmatch it return 0 .
else return 1(count increased by 1)

x%10 gives remainder when x is divided by 10
x/10 gives quotient when x is divided by 10

for example x=121 any y=221
call digitMatch(x/10,y/10) => digitMatch(121,221)

it starts with left most digit of x and y;
x%10 = 1
and y%10 = 1
and here (x%10==y%10)return 1

now we need to check whether next onward digits are same or not
means now we will check
x/10 = 12
y/10 = 22
here we call recursively 1+ digitMatch(x/10,y/10) => 1+ digitMatch(12,22)

next call:
x%10 = 2
and y%10 = 2
and here (x%10==y%10)return 1

now we will check number of digits matched in
x/10 = 1
y/10 = 2
here we call recursively return 1+digitMatch(x/10,y/10) => 1+ digitMatch(1,2)

next call:
x%10 = 1
and y%10 = 2
and here (x%10!=y%10)return 0
here x <10 and y<10
return 0 (No more call)

total match = 1+1+0 = 2 digits matched