concatenation

Why is the complexity of simple string concatenation O(n^2)?

由 自闭症网瘾萝莉.ら 提交于 2021-02-04 21:45:39
问题 I read on several manuals and online sources that the running time of "simple string concatenation" is O(n^2)? The algorithm is this: we take the first 2 strings, create a new string, copy the characters of the 2 original strings in the new string, and repeat this process over and over again until all strings are concatenated. We are not using StringBuilder or similar implementations: just a simple string concatenation. I think the running time should be something like O(kn) where k = number

Why is the complexity of simple string concatenation O(n^2)?

由 社会主义新天地 提交于 2021-02-04 21:44:07
问题 I read on several manuals and online sources that the running time of "simple string concatenation" is O(n^2)? The algorithm is this: we take the first 2 strings, create a new string, copy the characters of the 2 original strings in the new string, and repeat this process over and over again until all strings are concatenated. We are not using StringBuilder or similar implementations: just a simple string concatenation. I think the running time should be something like O(kn) where k = number

Concatenate multiple columns into one with dplyr

由 醉酒当歌 提交于 2021-02-04 21:10:52
问题 I have a df structured like this, but with a large number of columns and rows: A B C D 1 4 3 3 and I want to obtain a df with a single column, made by the concatenation of all the previous elements: A 1 B 4 C 3 D 3 How can I do? Better if solutions comprise the use of dplyr. 回答1: unlist and wrap it in data.frame data.frame(col = unlist(df), row.names = NULL) # col #1 A #2 1 #3 B #4 4 #5 C #6 3 #7 D #8 3 Or making it as tibble library(tibble) tibble(col = unlist(df)) # col # <fct> #1 A #2 1 #3

Concatenating two arrays with alternating values

由 ↘锁芯ラ 提交于 2021-02-04 14:19:06
问题 What is the best way to concatenate two arrays with alternating values? Let's say array1 is: [1, 3, 5, 7] array2 is: [2, 4, 6, 8] I want to combine these two arrays, so that the result is: [1, 2, 3, 4, 5, 6, 7, 8] In Java: int[] a1 = { 1, 3, 5, 7 }; int[] a2 = { 2, 4, 6, 8 }; int[] concat = new int[a1.length * 2]; for (int i = 0; i < concat.length; i++) { // concatenation } System.out.println(concat.toString()); // should be [1, 2, 3, 4, 5, 6, 7, 8] Update: No sorting is required, as the

Concatenating strings retrieved from form $_Post in php

由 有些话、适合烂在心里 提交于 2021-01-29 17:53:43
问题 I am posting a string through an HTML form with the following code: <html> <body> <form name="form" enctype="multipart/form-data" action="test.php" method="post"> <input name="message" type="text" value=""><br/><br/> <input type="submit" value="Upload"/><br/> </form> </body> </html> The code for test.php is the following: <?php $string1 = '$_POST["message"]'; $og_url = "http://thepropagator.com/facebook/testapp/issue.php?name=".$string1; echo $og_url; ?> The problem I'm having is that the

PHP String Concatenation With Variables [duplicate]

由 拥有回忆 提交于 2021-01-29 15:49:18
问题 This question already has answers here : How to combine two strings together in PHP? (17 answers) Closed last year . This is my first time doing this but I really had to, so I've been working with php and have this script that is giving me trouble when it goes to mail. All it is is an ajax POST request sending a code and email to the php script. The problem I am facing is getting the $message string for the first email to be concatenated with the variables. If I just set $message to a string

Allen Browne's ConcatRelated() Error 3061: Too few parameters

由 Deadly 提交于 2021-01-29 03:01:01
问题 I am trying to create a list of products at a given warehouse. Allen Browne's ConcatRelated() function seems to be the tried and true method to create lists using when a linked variable is the same, but I can't get it to work. I have broken my information down into a single query... "qry_Products" SELECT qry_AX_LineItems_LINES.Warehouse, tblREF_Chemical.[Sales Name] FROM qry_AX_LineItems_LINES INNER JOIN tblREF_Chemical ON qry_AX_LineItems_LINES.ItemId = tblREF_Chemical.[Item Number] GROUP BY

How do you “pivot” using conditions, aggregation, and concatenation in Pandas?

由 核能气质少年 提交于 2021-01-28 14:05:13
问题 I have a dataframe in a format such as the following: Index Name Fruit Quantity 0 John Apple Red 10 1 John Apple Green 5 2 John Orange Cali 12 3 Jane Apple Red 10 4 Jane Apple Green 5 5 Jane Orange Cali 18 6 Jane Orange Spain 2 I need to turn it into a dataframe such as this: Index Name All Fruits Apples Total Oranges Total 0 John Apple Red, Apple Green, Orange Cali 15 12 1 Jane Apple Red, Apple Green, Orange Cali, Orange Spain 15 20 Question is how do I do this? I have looked at the groupby

Concat causes stack overflow if called multiple times

由 断了今生、忘了曾经 提交于 2021-01-28 12:12:46
问题 Application accidentally crashed with stack overflow error. After research I found that the reason of crash is following code: foreach (var item in items) { result = result.Concat(item.Data); } This is concatenation of multiple IEnumerable s. Application crashed when items contained 10,000 elements. SelectMany fixed this issue. But still... Why Concat extension causes stack overflow here? 回答1: Remember that the result of Concat is not a collection - it's a query . So your "result" is

Reason for the inability to concatenate strings and ints in Python

由 允我心安 提交于 2021-01-28 05:30:58
问题 It is well documented in numerous that str is required to convert ints to strings before they can be concatenated: 'I am ' + str(n) + ' years old.' There must be a fundamental reason why Python does not allow 'I am ' + n + ' years old.' and I would like to learn what that reason is. In my project, I print a lot of numbers and end up with code like this. 'The GCD of the numbers ' + str(a) + ', ' + str(b) + ' and ' + str(c) + ' is ' + str(ans) + '.' It would be much prettier if I could drop
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