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.

一刷
题解：
首先把int[] 变为String[], 这样遍于sort
sort的原则是，对于String a和b, 如果a+b > b+a， 那么a在前。
然后StringBuilder 逐一append String[]中的元素。

public class Solution {
    public String largestNumber(int[] nums) {
        if(nums == null || nums.length == 0) return "";
        
        //convert int array to string array
        String[] s_num = new String[nums.length];
        for(int i=0; i<nums.length; i++){
            s_num[i] = String.valueOf(nums[i]);
        }
        
        //sort the string according to first character
        Arrays.sort(s_num, new Comparator<String>(){
            public int compare(String a, String b){
                String s1 = a+b;
                String s2 = b+a;
                return s2.compareTo(s1);//reverse
            }
        });
        
        if(s_num[0].charAt(0) == '0') return "0";//edge case, the input is a bunch of 0
        StringBuilder sb = new StringBuilder();
        for(String s: s_num) sb.append(s);
        return sb.toString();
    }
}

二刷
同一刷

public class Solution {
    public String largestNumber(int[] nums) {
        if(nums == null || nums.length == 0) return "";
        String[] s_num = new String[nums.length];
        for(int i=0; i<nums.length; i++){
            s_num[i] = String.valueOf(nums[i]);
        }
        Arrays.sort(s_num, new Comparator<String>(){
            public int compare(String a, String b){
                String s1 = a+b;
                String s2 = b+a;
                return s2.compareTo(s1);//reverse
            }
        });
        
        StringBuilder sb = new StringBuilder();
        if(s_num[0].charAt(0) == '0') return "0";
        for(String s:s_num){
            sb.append(s);
        }
        return sb.toString();
    }
}