recursion

问题 I have a function that I want to write in tail recursive form. The function calculates the number of ways to get the sum of k by rolling an s sided die n times. I have seen the mathematical solution for this function on this answer. It is as follows: My reference recursive implementation in R is: sum_ways <- function(n_times, k_sum, s_side) { if (k_sum < n_times || k_sum > n_times * s_side) { return(0) } else if (n_times == 1) { return(1) } else { sigma_values <- sapply( 1:s_side, function(j)

问题 Comp sci professor gave us this problem in our homework... I'm not sure how to proceed and the code I have written seems to be failing miserably. Here is the prompt: (binary to decimal) Write a recursive method that parses a binary number as a string into a decimal integer. The method header is: public static String bin2Dec(String binaryString) write a test program that prompts the user to enter a binary string and displays its decimal equivalent. Any help greatly appreciated. Here is my code

问题 Comp sci professor gave us this problem in our homework... I'm not sure how to proceed and the code I have written seems to be failing miserably. Here is the prompt: (binary to decimal) Write a recursive method that parses a binary number as a string into a decimal integer. The method header is: public static String bin2Dec(String binaryString) write a test program that prompts the user to enter a binary string and displays its decimal equivalent. Any help greatly appreciated. Here is my code

问题 Comp sci professor gave us this problem in our homework... I'm not sure how to proceed and the code I have written seems to be failing miserably. Here is the prompt: (binary to decimal) Write a recursive method that parses a binary number as a string into a decimal integer. The method header is: public static String bin2Dec(String binaryString) write a test program that prompts the user to enter a binary string and displays its decimal equivalent. Any help greatly appreciated. Here is my code

问题 The first method is OK. The second repeats constantly the same pair of numbers. It is quite obscure to me why... Could you point to the good direction ? module Normal = let rnd = new MersenneTwister() let sampleNormal = fun () -> let rec randomNormal() = let u1, u2 = rnd.NextDouble(),rnd.NextDouble() let r, theta= sqrt (-2. * (log u1)), 2. * System.Math.PI * u2 seq { yield r * sin theta; yield r * cos theta ; printfn "next";yield! randomNormal() } randomNormal() let sampleNormalBAD = fun () -

问题 I'm trying to get a result looking something like this: Miniors | Boys | 54kg - 62kg where every value delimited by a pipe | comes from an array containing a certain "type of restriction". For example: ageGroups, genders, weightClasses (as seen above). The way I'm able to get this result right now is if I hard code the nested forEach-loops (using underscorejs), but this means I have to now how many arrays I have to loop over to get wanted result. This works "fine": var categories = []; _.each

问题 I just can't wrap my head around recursion. I understand all of the concepts (breaking solution into smaller cases) and I can understand solutions after I read them over and over again. But I can never figure out how to use recursion to solve a problem. Is there any systematic way to come up with a recursive solution? Can someone please explain to me their thought process when they try to solve the following recursive problem: "Return all permutations of a string using recursion" . Here is an

问题 Suppose I have two lists with names, a = list( a=1, b=2, c=list( d=1, e=2 ), d=list( a=1, b=2 ) ) b = list( a=2, c=list( e=1, f=2 ), d=3, e=2 ) I'd like to recursively merge those lists, overwriting entries if the second argument contains conflicting values. I.e. the expected output would be $a [1] 2 $b [1] 2 $c $c$d [1] 1 $c$e [1] 1 $c$f [1] 2 $d [1] 3 $e [1] 2 Any hint? 回答1: I am not so sure if a custom function is necessary here. There is a function utils::modifyList() to perform this

问题 A common term in finance and reinforcement learning is the discounted cumulative reward C[i] based on a time series of raw rewards R[i] . Given an array R , we'd like to calculate C[i] satisfying the recurrence C[i] = R[i] + discount * C[i+1] with C[-1] = R[-1] (and return the full array C ). A numerically stable way of calculating this in python with numpy arrays might be: import numpy as np def cumulative_discount(rewards, discount): future_cumulative_reward = 0 assert np.issubdtype(rewards

问题 Can we make ff-find-other-file to search recursively in directories which are listed in ff-search-directories. Instead of searching only in /usr/include, it would also search in /usr/include/llvm. Or likewise. 回答1: I've added this function to my .emacs file: (defun get-all-subdirectories(dir-list) "Returns a list of all recursive subdirectories of dir-list, ignoring directories with names that start with . (dot)" (split-string (shell-command-to-string (concat "find " (mapconcat 'identity dir