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.

注意：

1. 这里的比较方法是如果 a + b > b + a 则 a > b ， 即 比较 30 和 34 , 因为 3034 < 3430， 所以34 比 30 大。

2. priorityqueue 默认是从小到大输出的。 所以在comparator里面 大的return -1！

public class Solution {

    public String largestNumber(int[] num) {
        PriorityQueue<Integer> pq = new PriorityQueue<Integer>(
            new Comparator<Integer>() {
                public int compare(Integer a, Integer b){
                    StringBuilder sb = new StringBuilder();
                    sb.append(a);
                    sb.append(b);
                    int first = Integer.valueOf(sb.toString());
                    sb = new StringBuilder();
                    sb.append(b);
                    sb.append(a);
                    int second = Integer.valueOf(sb.toString());
                    if(first > second) return -1;
                    else if(first == second) return 0;
                    else return 1;
                }
            }
        );
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < num.length; i ++){
            pq.add(num[i]);
        }
        for(int i = 0; i < num.length; i ++){
            sb.append(pq.poll());
        }
        return sb.charAt(0) == '0' ? new String("0") : sb.toString();
    }
}