#!/usr/bin/Rscript

find_missing_number <- function(list)
{
	numbers <- logical(length(list)+1)
	for(number in list) numbers[number] <- TRUE
	return(which(!numbers))
}

# same function, without using "which" (linear time is obvious here...)
find_missing_number_ <- function(list)
{
	numbers <- logical(length(list)+1)
	for(number in list) numbers[number] <- TRUE
	for(number in 1:length(numbers)) if(!numbers[number]) return(number)
}

# just for fun: the function written as short as possible (but sort() has non-linear time!)
find_missing_number_short <- function(list) which(diff(sort(c(0,list)))>1)

l <- sample(1:50, 49)
cat("unsorted list:", l, "\n")
cat("( sorted list:", sort(l), ")\n")
cat("missing number:", find_missing_number(l), "\n")