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.

[分析] 贪心思想，任两个数字字符串a, b, 若 a + b > b + a, 则a 应排在 b 前面。
注意点：
1.Arrays.sort()不支持给int数组传自定义比较器，因此需要转为String数组进行排序。
2.要判断并处理前缀为0的结果。

public class Solution {
    Comparator<String> comparator = new Comparator<String>() {
        public int compare(String a, String b) {
            String result1 = a + b;
            String result2 = b + a;
            return result1.compareTo(result2);
        }  
    };
    public String largestNumber(int[] nums) {
        if (nums == null || nums.length == 0)
            return "";
        int N = nums.length;
        String[] numstrs = new String[N];
        for (int i = 0; i < N; i++)
            numstrs[i] = String.valueOf(nums[i]);
        Arrays.sort(numstrs, comparator);
        StringBuilder sb = new StringBuilder();
        for (int i = N - 1; i >= 0; i--)
            sb.append(numstrs[i]);
        
        // truncate prefix 0 
        // style 1
/*        if (sb.charAt(0) == '0' && N > 1) {
            int j = 0;
            while (j < sb.length() - 1 && sb.charAt(j) == '0')
                j++;
            sb.delete(0, j);
        }
        return sb.toString();*/
        // style 2
        int i = 0;
        while (i < sb.length() && sb.charAt(i) == '0')
            i++;
        if (i == sb.length()) 
            return "0";
        else 
            return sb.substring(i, sb.length());
    }
}