179. Largest Number

 1     public String largestNumber(int[] nums) {
 2         if(nums == null || nums.length == 0)
 3             return "";
 4 
 5         // Convert int array to String array, so we can sort later on
 6         String[] s_num = new String[nums.length];
 7         for(int i = 0; i < nums.length; i++)
 8             s_num[i] = String.valueOf(nums[i]);
 9 
10         // Comparator to decide which string should come first in concatenation
11         Comparator<String> comp = new Comparator<String>(){
12             @Override
13             public int compare(String str1, String str2){
14                 String s1 = str1 + str2;
15                 String s2 = str2 + str1;
16                 return s2.compareTo(s1); // reverse order here, so we can do append() later
17             }
18         };
19 
20         Arrays.sort(s_num, comp);//由顶到底，前一个元素加后一个元素的值，大于后一个元素加前一个元素的值
21         // An extreme edge case by lc, say you have only a bunch of 0 in your int array
22         if(s_num[0].charAt(0) == ‘0‘)
23             return "0";
24 
25         StringBuilder sb = new StringBuilder();
26         for(String s: s_num)
27             sb.append(s);
28 
29         return sb.toString();        
30     }