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.

public class Solution {
    public String largestNumber(int[] nums) {
        if(nums==null||nums.length==0) return "";//corner case:if the input array is null or the length of array is zero
        // covert int array into string array so that we can sort it later
        String[] s_nums = new String[nums.length];
        for(int i=0;i<s_nums.length;i++){
            s_nums[i] = String.valueOf(nums[i]);
        }
        // Comparator to decide which string come first in concatenation
        Comparator<String> com = new Comparator<String>(){
            public int compare(String str1,String str2){
                String s1 = str1+str2;
                String s2 = str2+str1;
                return s2.compareTo(s1);
            }
        };
        // sort the string array
        Arrays.sort(s_nums,com);
        // an extreme edge case, to consider all of the int array elements are zero
        if(s_nums[0].charAt(0)=='0') return "0";
        StringBuilder sb = new StringBuilder();
        for(int i=0;i<s_nums.length;i++){
            sb.append(s_nums[i]);
        }
        return sb.toString();
    }
}
//As for the run time complexity,suppose the average string length is k,the comparator takes O(k)time,the sort takes nlongn time,so the total time costs knlongn time.As for the space complexity,O(n);