179. 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.

含义：给定多个非负数，将他们排列成一个最大数，用string返回

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

        // Convert int array to String array, so we can sort later on
        String[] s_num = new String[nums.length];
        for(int i = 0; i < nums.length; i++)
            s_num[i] = String.valueOf(nums[i]);

        // Comparator to decide which string should come first in concatenation
        Comparator<String> comp = new Comparator<String>(){
            @Override
            public int compare(String str1, String str2){
                String s1 = str1 + str2;
                String s2 = str2 + str1;
                return s2.compareTo(s1); // reverse order here, so we can do append() later
            }
        };

        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
        // An extreme edge case by lc, say you have only a bunch of 0 in your int array
        if(s_num[0].charAt(0) == '0')
            return "0";

        StringBuilder sb = new StringBuilder();
        for(String s: s_num)
            sb.append(s);

        return sb.toString();        
    }