摘要： You have nn lights, each with its own button, in a line. Pressing a light’s button will toggle that light’s state; if the light is on, it will turn of 阅读全文

摘要： You are given a rooted tree with n nodes. The nodes are numbered 1..n. The root is node 1, and m of the nodes are colored red, the rest are black. You 阅读全文

摘要： Given a registry of all houses in your state or province, you would like to know the minimum size of an axis-aligned square zone such that every house 阅读全文

摘要： Consider n initial strings of lower case letters, where no initial string is a prefix of any other initial string. Now, consider choosing k of the str 阅读全文