int singleNumber(vector<int> &A) {
// write your code here
if (A.empty())
return 0;
int result = A[0];
for (int i = 1; i < A.size(); i++)
{
result = result ^ A[i];
}
return result;
}
原文：http://www.cnblogs.com/dragonfive/p/6517283.html