Largest Number leetcode

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.

对于arraylist 用Collection.sort(arraylist, comparator) array用 Arrays.sort(array, comparator)

a.compareTo(b) 如果a大 return +, 小return - , eq return=

public class Solution {
    public String largestNumber(int[] nums) {
        if (nums == null || nums.length == 0) {
            return "";
        }
        String[] str = new String[nums.length];
        for (int i = 0; i < nums.length; i++) {
            str[i] = String.valueOf(nums[i]);
        }
        Arrays.sort(str, new Comparator() {
            public int compare(String s1, String s2) {
                String l1 = s1 + s2;
                String l2 = s2 + s1;
                return l2.compareTo(l1);//为了使数值大的排在前面
            }
        });
        StringBuilder sb = new StringBuilder();
        for (String s : str) {
            sb.append(s);
        }
        if (sb.charAt(0) == '0') {
            return "0";
        }
        return sb.toString();
    }
}