Understanding of fast and slow pointer

low = fast when , Fast and slow hands meet ,low The distance traveled is the initial point （0） To the point where the ring starts （x） add Point at which the ring starts （x） To the meeting point （y） This distance , and fast The distance traveled is Starting point （0） To the point where the ring starts （x）, spot （x） point-to-point （y）, spot （y） point-to-point （x）, spot （x） point-to-point （y）. Again because fast The distance traveled is low Twice as many , set up 0 To x The length is a,x To y The length is b, Then there are 2*（a+b） = a+ b+ (y To x Distance of ) + b, be y To x The distance is equal to 0 To x Distance of . So when the new two pointers A from 0 set out , One from the meeting point y When we set out , The same value they come to is the starting point of the ring , namely x spot .