Single Number

Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

public class Solution {
    public int singleNumber(int[] A) {
          if(A.length<=0)
            return -1;
        if(A.length==1)
            return A[0];
      //  Arrays.sort(A);
        Arrays.sort(A);
        int j  = 0 ;
        for (int i=0;i<A.length-1;i++){
            if(A[i]==A[i+1])
                j++;
            else {
                if(j<1)
                    return A[i];
                j = 0;
            }

        }
    return A[A.length-1];
    }
}