Sorry, I google it and can not find enough explanation..
Can any one explain that to me?
One pass means that you can only traverse the link list from head to tail for only ONE time.
Your pointer points to 1 at first. Then it move to 2, and 3, and 4. That's the end.
You cannot try to traverse the link node any more.
I think one pass means the time should be O(n) and the memory should be constant. For your reference, here is a wikipedia link, https://en.wikipedia.org/wiki/One-pass_algorithm.
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