Think Like a Machine!

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How many positive integers less than 1 000 000 become bigger when their digits are reversed?

The answer is 449001.

1 solution

Alex Zhong
Apr 10, 2015

python program

def reverse_int(n):

    return int(str(n)[::-1])

i = 0

  for n in range(1,1000000):

      if reverse_int(n) > n:

          i=i+1

print (i)

How are 1 digit numbers reversed (along with 2,3,4 and 5 digit numbers)? i.e. would 000 001 $\rightarrow$ 100 000 or would we have 1 $\rightarrow$ 1 because I was thinking of using group theory to think of the digits being reversed as a functions of at most order 2 ( $f^{2} (x) = x$ ) . i.e. 1 = 000 001 $\rightarrow$ 100 000 $\rightarrow$ 000 001

Curtis Clement - 6 years, 2 months ago

I think it is $1 \rightarrow 1$ .

Alex Zhong - 6 years, 2 months ago

Think Like a Machine!

The answer is 449001.

1 solution

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