ex:
public static int fibb (int n) {
if(n==0||n==1)
return 1;
else{
return fibb(n-1)+fibb(n-2);
}
}
How will the line fibb(n-1)+fibb(n-2) be executed .. like will fibb(n-1) finish first the fibb(n-2) starts or how exactly, I'm fairly new to recursion and can't seem to wrap my head around how it works.
Help appreciated.
First, the recursive calls will be executed (the order in which being dependent on your programming language), then their results will be summed together.
fibb(3) returns fibb(2) + fibb(1)
fibb(2) returns fibb(1) + fibb (0)
so you get 1 + 1 + 1 = 3
fibb(4) returns fibb(3) + fibb(2), we know fibb(3) returns three from above,
fibb(2) returns fibb(1) + fibb(0) also from above,
so fibb(4) returns 3 + 2 = 5
It's important to notice that with this implementation you must computer each previous Fibonacci number twice. Which means by the time you get to around ~20 (guess) it's going to get VERY slow.
Related
I would like to compute Jaccard Similarity on text using R.
I already found a way to compute JS using a function. Which works fine when I apply it stand-alone.
I have a dataset with utterances in conversation. I would like to add a column that presents the Jaccard similarity of each utterance with the (immediate) previous one.
Like I said I already use a function to compute JS.
jaccard <- function(a, b) {
intersection = length(intersect(a, b))
union = length(a) + length(b) - intersection
return (intersection/union)
}
I have already tried multiple things looking like this:
Text$J <- 0
# for every row in DT
for (i in 1:length(Text)) {
if(i==1) {
#using NA at first line
Text[i,2] <- NA
} else {
Text$J <- jaccard(Text$Utterance,Text$Utterance[i-1])
}
}
Is it possible to integrate a function like the above in a 'for every row' code? So far, my attempts are not successful, but that might be me. What happens in most cases is that is just pastes one Jaccard value to the whole column. Thank you in advance!
I had the task to code the following:
Take a list of integers and returns the value of these numbers added up, but only if they are odd.
Example input: [1,5,3,2]
Output: 9
I did the code below and it worked perfectly.
numbers = [1,5,3,2]
print(numbers)
add_up_the_odds = []
for number in numbers:
if number % 2 == 1:
add_up_the_odds.append(number)
print(add_up_the_odds)
print(sum(add_up_the_odds))
Then I tried to re-code it using function definition / return:
def add_up_the_odds(numbers):
odds = []
for number in range(1,len(numbers)):
if number % 2 == 1:
odds.append(number)
return odds
numbers = [1,5,3,2]
print (sum(odds))
But I couldn’t make it working, anybody can help with that?
Note: I'm going to assume Python 3.x
It looks like you're defining your function, but never calling it.
When the interpreter finishes going through your function definition, the function is now there for you to use - but it never actually executes until you tell it to.
Between the last two lines in your code, you need to call add_up_the_odds() on your numbers array, and assign the result to the odds variable.
i.e. odds = add_up_the_odds(numbers)
def listc(favn):
num = 0
while num < favn :
num += 1
return num
list = []
i = int(raw_input("Input your favourite number : > "))
for num in range(0,i):
list.append(listc(i))
print list
The elements of the list are just same. Little iterations in code are sometime printing [None] in list also.
I want to generate a list with content as 1 to i.
There are two issues with your code.
First the while loop does not run 'favn' no. of times because the return statement is within while loop.It just runs single time, and everytime it returns 1.
Also, you should change
for num in range(0,i):
list.append(listc(i))
to
for num in range(0,i):
list.append(listc(num))
You will get the output you wanted.
If you want to generate a list from 1 to i, you can simply do list = range(1, i + 1).
I want to avoid importing different modules as that is mostly what I have found while looking online. I am stuck with this bit of code and I don't really know how to fix it or improve on it. Here's what I've got so far.
def avg(lst):
'''lst is a list that contains lists of numbers; the
function prints, one per line, the average of each list'''
for i[0:-1] in lst:
return (sum(i[0:-1]))//len(i)
Again, I'm quite new and this for loops jargon is quite confusing to me, so if someone could help me get it so the output of, say, a list of grades would be different lines containing the averages. So if for lst I inserted grades = [[95,92,86,87], [66,54], [89,72,100], [33,0,0]], it would have 4 lines that all had the averages of those sublists. I also am to assume in the function that the sublists could have any amount of grades, but I can assume that the lists have non-zero values.
Edit1: # jramirez, could you explain what that is doing differently than mine possible? I don't doubt that it is better or that it will work but I still don't really understand how to recreate this myself... regardless, thank you.
I think this is what you want:
def grade_average(grades):
for grade in grades:
avg = 0
for num in grade:
avg += num
avg = avg / len(grade)
print ("Average for " + str(grade) + " is = " + str(avg))
if __name__ == '__main__':
grades = [[95,92,86,87],[66,54],[89,72,100],[33,0,0]]
grade_average(grades)
Result:
Average for [95, 92, 86, 87] is = 90.0
Average for [66, 54] is = 60.0
Average for [89, 72, 100] is = 87.0
Average for [33, 0, 0] is = 11.0
Problems with your code: the extraneous indexing of i; the use of // to truncate he averate (use round if you want to round it); and the use of return in the loop, so it would stop after the first average. Your docstring says 'print' but you return instead. This is actually a good thing. Functions should not print the result they calculate, as that make the answer inaccessible to further calculation. Here is how I would write this, as a generator function.
def averages(gradelists):
'''Yield average for each gradelist.'''
for glist in gradelists:
yield sum(glist) /len(glist)
print(list(averages(
[[95,92,86,87], [66,54], [89,72,100], [33,0,0]])))
[90.0, 60.0, 87.0, 11.0]
To return a list, change the body of the function to (beginner version)
ret = []
for glist in gradelists:
ret.append(sum(glist) /len(glist))
return ret
or (more advanced, using list comprehension)
return [sum(glist) /len(glist) for glist in gradelists]
However, I really recommend learning about iterators, generators, and generator functions (defined with yield).
I'm trying to split an HTML document into its head and body:
my #contentsArray = split( /<\/head>/is, $fileContents, 1);
if( scalar #contentsArray == 2 ){
$bodyContents = $dbh->quote(trim($contentsArray[1]));
$headContents = $dbh->quote(trim($contentsArray[0]) . "</head>");
}
is what i have. $fileContents contains the HTML code. When I run this, it doesn't split. Any one know why?
The third parameter to split is how many results to produce, so if you want to apply the expression only once, you would pass 2.
Note that this does actually limit the number of times the pattern is used to split the string (to one fewer than the number passed), not just limit the number of results returned, so this:
print join ":", split /,/, "a,b,c", 2;
outputs:
a:b,c
not:
a:b
sorry, figured it out. Thought the 1 was how many times it would find the expression not limit the results. Changed to 2 and works.