Why doesn't this code work (Leetcode in Python)? - 


class solution:     def ishappy(self, n):         list_n, l, ls, num = [n,], 0, 0, 0         while num != 1:             if l != ls:                 return false             num = sum([int(i)**2 in list(str(n))])             list_n.append(num)             l, ls = len(list_n), len(set(list_n))         return true

input: 7

output: false

expected: true

it's happy number | leetcode oj

write algorithm determine if number "happy".

a happy number number defined following process: starting positive integer, replace number sum of squares of digits, , repeat process until number equals 1 (where stay), or loops endlessly in cycle not include 1. numbers process ends in 1 happy numbers.

to answer question: code fails because you're confusing num , n. in particular, compute num n, , neither ever changes. rid of 1 of them, less confusing. should learn debug, btw... printing num or n inside loop have made clear what's happening.

using set btw easier , faster, try well. here's 1 way:

def ishappy(n):     stop = {1}     while n not in stop:         stop.add(n)         n = sum(int(d)**2 d in str(n))     return n == 1

and here's 1 uses 2 single ints. can see how works?

def ishappy(n):     s = lambda n: sum(int(d)**2 d in str(n))     m = s(n)     while m != n:         n, m = s(n), s(s(m))     return n == 1

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