Leetcode: Largest Number

Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.

Note: The result may be very large, so you need to return a string instead of an integer.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

Understand the problem:
The problem suggests to sort the array first according to the lexco order. The sorting rule is if two strings a and b, we compares ab and ba, and sort it in descending order.

The only thing needs to take care is the leading zeros in the final results. If there are leading zeros, it must be the case like 0, 0, 0, 0 ... i.e all array elements must be 0. In this case, return "0".

Code (Java):

public class Solution {
    public String largestNumber(int[] nums) {
        if (nums == null || nums.length == 0) {
            return "";
        }
        String[] strs = new String[nums.length];
        for (int i = 0; i < strs.length; i++) {
            strs[i] = String.valueOf(nums[i]);
        }
        
        Arrays.sort(strs, new StringComparator());
        
        StringBuffer sb = new StringBuffer();
        
        for (String str : strs) {
            sb.append(str);
        }
        
        if (sb.charAt(0) == '0') {
            return "0";
        }
        
        return sb.toString();
    }
    
    public class StringComparator implements Comparator<String> {
        @Override
        public int compare (String str1, String str2) {
            String ab = str1 + str2;
            String ba = str2 + str1;
            return ba.compareTo(ab);
        }
    }
}