[LeetCode179]Largest Number

题目：

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.

思路：将数字按照最高位的大小排序，然后连接成字符串即可

代码：

public class Solution {
    public string LargestNumber(int[] nums) {
        Array.Sort(nums,CompareByTopDigit);
        if(nums[nums.Length-] == ) return "";
        string s = "";
        for(int i = nums.Length - ; i >= ; i--)
        {
            s += nums[i].ToString();
        }
        return s;
    }

    public int CompareByTopDigit(int a, int b)
    {
        return (a + "" + b).CompareTo(b + "" + a);
    }
}