数据结构讲义7.ppt

Data Structure Software College Northeastern University Chapter 7 Searching Overview Searching Problem Static Searching problem Binary Search Tree AVL Tree 7.1 Searching Problem Search Table - An collect of objects for being searched Type - static search table(静态有哪些信誉好的足球投注网站表): the table to be searched is never altered - dynamic search table(动态有哪些信誉好的足球投注网站表): the table to be searched can be altered Attributes - key（关键字）: A group of one or more attributes that uniquely identifies an object. Searching Problem Searching problem Give a key value X and a search table A, return the position of X in A or an indication that is not presented. If X occurs more than once, return any occurrence. Searching Problem The complexity of searching algorithms The number of comparisons - unsuccessful search - The worse-case successful search - The average of search（AVL-平均比较次数） Static Searching Problem different searching algorithms: Sequential search(顺序有哪些信誉好的足球投注网站), Block search（块有哪些信誉好的足球投注网站）, Binary search（二分有哪些信誉好的足球投注网站） 7.2 Static Searching Problem: Sequential Searching(顺序有哪些信誉好的足球投注网站) Storage search table: Array with unsorted objects Algorithm - Sequential Searching - Steps through the array sequentially until a match is found or reaching the end of array 7.3 Binary Search A sequential search of a list begins at the beginning of the list and continues until the item is found or the entire list has been searched A binary search looks for an item in a list using a divide-and-conquer strategy Meaning of Divide and Conquer In military, “divide and conquer” is a kind of strategy. In computer science, “divide and conquer” is a programming technique by breaking down a problem into one or more sub problems. “Divide and conquer” is usually implemented by recursion. Structure of Divide and Conquer Divide Break a problem into sub problem(s) Conquer Solve all sub problem(s) Combine Solve the problem using the results of the sub problem(s) Binary Search: Example Binary Search: Example Binary Search: