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.

其实问题可以转化为数组排序，排序的依据是例如3和30，330大于303于是3应该排在30的前面，至于如何比较可以直接使用String的compareTo()方法。其中需要注意的细节是数组全为0的情况。代码如下：

public class Solution {
    
    //判断a，b的位置，a在b之前返回true否则返回false
    public boolean compare(int a,int b) {
        String s1 = String.valueOf(a);
        String s2 = String.valueOf(b);
        String sum1 = s1+s2;
        String sum2 = s2+s1;
        if(sum1.compareTo(sum2)>=0) return true;
        else return false;
    }
    
    public String largestNumber(int[] num) {
        String re = "";
        int size = num.length;
        //冒泡排序，每次将最小的沉底
        for(int i=0;i<size-1;i++) {
            for(int j=0;j<size-i-1;j++) {
                if(!compare(num[j],num[j+1])) {
                    int tmp = num[j];
                    num[j] = num[j+1];
                    num[j+1] = tmp;
                }
            }
        }
        int sum = 0;
        for(int k=0;k<size;k++) {
            sum+=num[k];
            re = re+num[k];
        }
        if(sum==0){
            re = "0";
        }
        return re;
    }
}