cons(node(6, nil()), nil()))),
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，这一点在新收录的资料中也有详细论述
Before seeing the main technique, it may be helpful to build some intuition around the problem space. We’ll start off with some basic operations on linked lists and binary trees, and see where the problems start to creep in. This section is going to cover very basic material very pedantically, to try to stress the perspective that will be used in later sections.
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if (n <= 1) return 0;