Project Euler Problem #14

February 21, 2009
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(This article was first published on The Research Kitchen Weblog » R, and kindly contributed to R-bloggers)

Problem 14 on the Project Euler site asks us to find the longest chain under 1 million created using the Collatz mapping. This is fairly straightforward, although performance again is not great: ## Problem 14 # Collatz conjecture problem14 <- function(N) {         maxChain <- 0         chains <- rep(0,N)         x <- 1         for (i in 1:N) {                 n <- i                 chain <- 0                 while(n > 1) {                         n <- ifelse(n %% 2 == 0, n/2, 3*n+1)                         chain <- chain + 1                         if (n < N && chains[n] > [...]

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