179.Largest Number

1- Sort + Custom Comparator

The Comparator is very new!!

class Solution {
    public String largestNumber(int[] nums) {
        List<String> list = new ArrayList<>();
        for(Integer i : nums){
            list.add(i.toString());
        }
        Collections.sort(list, new Comparator<String>(){
            @Override
            public int compare(String s1, String s2){
                String cat1 = s2 + s1;
                String cat2 = s1 + s2;
                return cat1.compareTo(cat2);
            }
        });
        //in case of: [0,0] -> "00"
        if(list.get(0).equals("0"))
            return "0";
        StringBuilder sb = new StringBuilder();
        for(String s : list){
            sb.append(s);
        }
        return sb.toString();
    }
}