Adds one space character after the element unless its the last element. But this solution is invalid anyway. It doesn't return pairs but single Strings instead with the comma at the right place so it passes the tests which unfortunately make use of Arrays.deepToString instead of comparing the array contents directly.

Hi, I undstand everyline but these
if(j != arr.length - 1)
a[i][0] += " ";

can anyone explain it ?