Largest Number

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

 Notice

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

Example

Given [1, 20, 23, 4, 8], the largest formed number is 8423201.

分析：

这里把所有的数转换成string, 然后排序。但是string怎么比较大小呢？这里不能用一般比较方法，需要比较str1+str2 和str2 + str1 来确定哪个大。

public class Solution {
    public String largestNumber(int[] num) {
        if (num == null || num.length == 0) return "";

        String[] strNum = new String[num.length];
        for (int i = 0; i < num.length; i++) {
            strNum[i] = String.valueOf(num[i]);
        }

        Arrays.sort(strNum, (String str1, String str2) -> (str1 + str2).compareTo(str2 + str1));
        StringBuilder sb = new StringBuilder();

        for (int i = strNum.length - 1; i >= 0; i--) {
            sb.append(strNum[i]);
        }
        
        while (sb.length() > 1 && sb.charAt(0) == '0') {
            sb.deleteCharAt(0);
        }
        return sb.toString();
    }
}