SingleNumber

//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 SingleNumber {
public int singleNumber(int[] A) {
       int a=A[0];
       for(int i=1;i          a=a^A[i];//异或
        return a;
   }
}