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Programming Articles
Page 1249 of 2547
Count square and non-square numbers before n in C++
We are given a number N. The goal is to find ordered pairs of positive numbers such that the sum of their cubes is N.Naive ApproachTraverse all numbers from 1 to N and check if it is a perfect square. If floor(sqrt(i))==ceil(sqrt(i)).Then the number is a perfect square.Efficient ApproachPerfect squares below N can be found using formula: floor(sqrt(N)).Let’s understand with examples.Input N=20Output Count of square numbers: 4 Count of non-square numbers: 16Explanation Square numbers are 1, 4, 9 and 16. Rest all are non-squares and less than 20.Input N=40Output Count of square numbers: 6 Count of non-square numbers: 34Explanation Square numbers are 1, 4, 9, 16, ...
Read MoreHow to subset nth row from an R data frame?
We can find subsets using many ways in R and the easiest way is to use single-square brackets. If we want to subset a row or a number of consecutive or non-consecutive rows then it can be directly done with the data frame name and the single-square brackets. For example, if we have a data frame called df and we want to subset 1st row of df then we can use df[1, ] and that’s it.ExampleConsider the below data frame:> set.seed(214) > x y z a b c q w df1 df1Outputx y z a b c q w 1 ...
Read MoreHow to convert a named vector to a list in R?
A named vector cannot be directly converted to a list because we would need to un-name the vector names and convert those names to names of the list elements. This can be done by using lapply function function. For example, suppose we have a named vector x then it can be converted to a list by using the command x x1 names(x1) x1OutputA B C D E F G H I J K L M N O P Q R S T U V W X Y Z 1 2 3 4 5 6 7 8 9 10 11 12 ...
Read MoreCount strings that end with the given pattern in C++
We are given an array of strings str[] and a pattern string pat. The goal is to find the string elements of str[] that have pattern pat at the end.We will traverse each string of str and compare last characters with pat. If they match incrementLet’s understand with examples.Input str[]={ “kittens”, “hens”, “deers”, “dogs” } pat=”ens”Output Strings that end with given pattern: 2Explanation Strings “kitt-ens” and “h-ens” end with “ens”.Input str[]={ “tickets”, “wickets”, “bats”, “cricket” } pat=”et”Output Strings that end with given pattern: 1Explanation Strings “wick-et” ends with “et”.Approach used in the below program is as followsWe string array str[] and a pattern string pat.N is ...
Read MoreCount Primes in Ranges in C++
We are given range variables START and END. The goal is to find the count of prime numbers in the range [START, END].We will check if number i in range is prime by checking if any number other than 1 fully divides it and is between 1 and i/2. If it is prime. Increment count.Let’s understand with examples.Input Start=1 End=20Output Primes in Ranges : 8Explanation Primes between 1 and 20 are: 2, 3, 5, 7, 11, 13, 17, 19.Input Start=100 End=200Output Primes in Ranges : 21Explanation Primes between 100 and 200 are: 101 103 107 109 113 127 131 137 139 149 151 157 163 167 ...
Read MoreCount quadruples from four sorted arrays whose sum is equal to a given value x in C++
We are given four arrays A[], B[], C[] and D[]. The goal is to find all quadruples of elements of these arrays such that A[i]+B[j]+C[k]+D[l] =x. All four arrays have the same number of elements N.We will do this by traversing each array once and compare if A[i]+B[j]+C[j]+D[l]==x. If true increment count.Let’s understand with examples.Input A[]={ 1, 2, 3}; B[]={ 2, 3, 2}; C[]={ 4, 3, 1}; D[]={ 3, 1, 1 }; X=12Output Count of Quadruples: 4Explanation Quadruples such as ( A[i] B[j] C[k] D[l] ) are: (2 3 4 3) , (3 2 4 3), (3 3 3 3), (3 2 4 ...
Read MoreCount numbers whose sum with x is equal to XOR with x in C++
We are a number X. The goal is to find numbers between 0 and X whose sum with X is equal to XOR with X.We will do this by traversing no. from i=0 to i
Read MoreCount numbers whose XOR with N is equal to OR with N in C++
We are a number N. The goal is to find numbers between 0 and N whose OR with N is equal to XOR with N.We will do this by traversing no. from i=0 to i
Read MoreWhat is the difference between $ and @ in R?
If we have a data frame defined as df that contains column x, y, and z then extraction of these columns from df can be done by using df$x, df$y, and df$z. On the other hand, if we have an S4 object defined as Data_S4 that contains column x, y, and z then the extraction of these columns can be done by using Data_S4@x, Data_S4@y, and Data_S4@z.Example of a data frame:Example> x1 x2 df dfOutput x1 x2 1 4 2 2 7 0 3 10 2 4 3 1 5 7 1 6 2 2 7 3 4 8 4 ...
Read MoreCount number of ways to divide a number in parts in C++
We are given a positive number N. The goal is to count the number of ways in which the number N can be divided into 3 parts. The parts may or may not be equal. N lies in range [1, 5000].We will do this by using three for loops for 3 parts of the number. Check at the innermost loop that the sum of all three is equal to N. If true, then increment the count of ways.Let’s understand with examples.Input − N=5Output − Number of ways to divide N in 3 parts: 2Explanation − 5 can be shown as ...
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