int countSort(int n) {
		if (n==0) return 0;
		int[] count=new int[10];
		while (n!=0) {
			++count[n%10];
			n/=10;
		}
		StringBuilder s=new StringBuilder();
		for (int i=9;i>=0;--i)
			for (int j=0;j<count[i];++j) s.append(i);
		return Integer.parseInt(s.toString());
	}