binary-search | 易学教程

Collections.binarySearch(List list, K key) clarification. Java

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问题 Given the following statement, taken from this Oracle java tutorial, related to the binarySearch() method of the class Collections: The return value is the same for both forms. If the List contains the search key, its index is returned. If not, the return value is (-(insertion point) - 1) , where the insertion point is the point at which the value would be inserted into the List, or the index of the first element greater than the value or list.size() if all elements in the List are less than

how to apply binary search O(log n) on a sorted linked list?

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问题 Recently I came across one interesting question on linked list. Sorted singly linked list is given and we have to search one element from this list. Time complexity should not be more than O(log n) . This seems that we need to apply binary search on this linked list. How? As linked list does not provide random access if we try to apply binary search algorithm it will reach O(n) as we need to find length of the list and go to the middle. Any ideas? 回答1: It is certainly not possible with a

Calculating mid in binary search

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问题 I was reading an algorithms book which had the following algorithm for binary search: public class BinSearch { static int search ( int [ ] A, int K ) { int l = 0 ; int u = A. length −1; int m; while (l <= u ) { m = (l+u) /2; if (A[m] < K) { l = m + 1 ; } else if (A[m] == K) { return m; } else { u = m−1; } } return −1; } } The author says "The error is in the assignment m = (l+u)/2; it can lead to overflow and should be replaced by m = l + (u-l)/2 ." I can't see how that would cause an

Binary Search in Array

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How would I implement a binary search using just an array? Ensure that your array is sorted since this is the crux of a binary search. Any indexed/random-access data structure can be binary searched. So when you say using "just an array", I would say arrays are the most basic/common data structure that a binary search is employed on. You can do it recursively (easiest) or iteratively. Time complexity of a binary search is O(log N) which is considerably faster than a linear search of checking each element at O(N). Here are some examples from Wikipedia: Binary Search Algorithm : Recursive:

What is the difference between Linear search and Binary search?

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问题 What is the difference between Linear search and Binary search? 回答1: A linear search looks down a list, one item at a time, without jumping. In complexity terms this is an O(n) search - the time taken to search the list gets bigger at the same rate as the list does. A binary search is when you start with the middle of a sorted list, and see whether that's greater than or less than the value you're looking for, which determines whether the value is in the first or second half of the list. Jump

Bash Script Binary Search

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问题 Write a bash script to do a binary search. Read student names and grades from a file into an array. Prompt the user for a student name. Find the name in the array and display the grade. The data in the file is below: Ann:A Bob:C Cindy:B Dean:F Emily:A Frank:C Ginger:D Hal:B Ivy:A Justin:F Karen:D I have done the following but I am stuck on what to do next #!/bin/bash echo "please enter students Name: " read student echo "$student + $Grade" ((i=0)) while read students[$i] ; do ((i++)) done <

Finding multiple entries with binary search

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问题 I use standard binary search to quickly return a single object in a sorted list (with respect to a sortable property). Now I need to modify the search so that ALL matching list entries are returned. How should I best do this? 回答1: Well, as the list is sorted, all the entries you are interested in are contiguous . This means you need to find the first item equal to the found item, looking backwards from the index which was produced by the binary search. And the same about last item. You can

Which is faster, Hash lookup or Binary search?

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问题 When given a static set of objects (static in the sense that once loaded it seldom if ever changes) into which repeated concurrent lookups are needed with optimal performance, which is better, a HashMap or an array with a binary search using some custom comparator? Is the answer a function of object or struct type? Hash and/or Equal function performance? Hash uniqueness? List size? Hashset size/set size? The size of the set that I'm looking at can be anywhere from 500k to 10m - incase that

Binary Search in Javascript

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I'm trying to implement a binary search algorithm in JavaScript. Things seem okay, but my return statements appear to be returning undefined? Can anybody tell what's wrong here? Fiddle: http://jsfiddle.net/2mBdL/ Thanks. var a = [ 1, 2, 4, 6, 1, 100, 0, 10000, 3 ]; a.sort(function (a, b) { return a - b; }); console.log('a,', a); function binarySearch(arr, i) { var mid = Math.floor(arr.length / 2); console.log(arr[mid], i); if (arr[mid] === i) { console.log('match', arr[mid], i); return arr[mid]; } else if (arr[mid] < i && arr.length > 1) { console.log('mid lower', arr[mid], i); binarySearch

Implement binary search in objects

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问题 Is there any way to implement binary search in a ArrayList with objects? In this example the ArrayList will be sorted with the field 'id'. class User{ public int id; public string name; } ArrayList<User> users = new ArrayList<User>(); sortById(users); int id = 66 User searchuser = getUserById(users,id); How would the "User getUserById( ArrayList users, int userid )" look like if I it should return the user with a specified id using binary search? Is this even possible? 回答1: The Object