Let say we have N number and N is odd. Among the N numbers, two of them equal to each other except one. For example, let's say we have 7 numbers, which could be 5, 3, 4, 1, 3, 5, 1. Only 4 is distinct, other number always has anther one member equal to it. Then how can we design a algorithm to find the distinct number(among N numbers) in linear time with only one variable introduced.