Lecture 9 — March 4 , 2010
نویسندگان
چکیده
Last lecture we defined the Least Common Ancestor (LCA) and Range Min Query (RMQ) problems. Recall that an LCA query asks for the deepest node in a given rooted tree which is an ancestor of each of two query nodes, while an RMQ query asks for the minimal value stored in some contiguous subarray of a given array. We showed last lecture that an LCA query is nothing more than an RMQ query on an Euler tour of the given tree (where the value assigned to any node is its depth in the tree). Moreover, this array has the property that the difference between any pair of consecutive elements is ±1. Thus if we could solve the RMQ problem for so-called “±1 arrays” we could solve LCA.
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