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public class Solution {
    public String largestNumber(int[] nums) {
        if(nums==null||nums.length==0) return "";
        int n = nums.length;
        String[] numStrings = new String[n];
        for(int i=0; i<n; i++){
            numStrings[i] = String.valueOf(nums[i]);
        }
        Arrays.sort(numStrings, (a,b)->(b+a).compareTo(a+b));
        if(numStrings[0].charAt(0)=='0') return "0";
        StringBuilder sb = new StringBuilder();
        for(String numString:numStrings){
            sb.append(numString);
        }
        return sb.toString();
    }
}

public class Solution {
    //mergesort
    public String largestNumber(int[] nums) {
        int n;
        for(n=0;n<nums.length;n++)
        {
            if(nums[n]!=0)
            break;
        }
        if(n==nums.length)
        return new String("0");
        mergesort(nums);
        StringBuilder s = new StringBuilder();
        for(int i=0;i<nums.length;i++)
        {
           s.append(nums[i]);
        }
        return s.toString();
    }
    	public void mergesort(int[] A) {
		int n = A.length;
		if (n < 2)
			return;
		int mid = n / 2, i;
		int[] l = new int[mid], r = new int[n - mid];
		for (i = 0; i < mid; i++)
			l[i] = A[i];
		for (int j=0; j < r.length; j++)
			r[j] = A[i++];
		mergesort(l);
		mergesort(r);
		merge(l, r, A);
	}

	public void merge(int[] l, int[] r, int[] A) {
	int x=l.length, y = r.length,i=0, j=0, k=0;
	while(i<x && j<y)
	{
		if(compare(l[i],r[j]))
			A[k++]=r[j++];
		else
			A[k++]=l[i++];
	}
	while(j<y)
		A[k++]=r[j++];
	while(i<x)
		A[k++]=l[i++];
}
    public boolean compare(int a, int b)
    {
        if(a == 0 && b!=0)
        return true;
        else if(a!=0 && b==0)
        return false;
        int i = (int)Math.log10(a)+1, j = (int)Math.log10(b)+1;
        if(i==j && a<b)
        return true;
        else if(i==j && a>b)
        return false;
        else
        return (a*Math.pow(10,j)+b) < (b*Math.pow(10,i)+a);
    }
}

public class Solution {
     public String largestNumber(int[] num) {
		if(num == null || num.length == 0)
		    return "";
		
		// Convert int array to String array, so we can sort later on
		String[] s_num = new String[num.length];
		for(int i = 0; i < num.length; i++)
		    s_num[i] = String.valueOf(num[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);
                // 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();
		
	}
}