How can I solve this odd/even loop question (hailstone sequence)?

2015 9 22
2 个回答
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更新时间：2015 9 22
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0 个投票

n = 71
If n is even, divide it by 2 to get n / 2.
If n is odd, multiply it by 3 and add 1 to obtain 3n + 1.
Repeat process until n = 1.
I need to find out how many steps it takes to reach 1..
thanks!

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Thorsten
Thorsten 2015-9-22
What have you tried so far? Where did you got stuck?
ok, so im really new to matlab, but this is what i tried doing:
n(1,1) = 71;
iterations(1,1) = 0;
ii=1;
while n(1,ii)==1;
if mod(n(1,ii),2)==1
(3*n(1,ii))+1;
else n(1,ii)/2;
ii=ii+1;
end
iterations(1,ii) = iterations(1,ii) + 1;
end

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Varun Pai
Varun Pai 2015-9-22

0 个投票

I think this is your requiremnt. Please check
num = 71;
count = 0;
while(num~=1)
count = count+1;
if(mod(num,2)==0)
num = num/2;
else
num = 3*num + 1;
end
end
fprintf('count = %d', count);

更多回答（1 个）

Thorsten
Thorsten 2015-9-22

1 个投票

First you can skip the 1, and just write n(ii).
Next you have forgotten to assign the new value, and you have to move the increment of ii outside the else-clause
if mod(n(ii),2)==1
n(ii+1) = 3*n(ii)+1;
else
n(ii+1) = n(ii)/2;
end
ii=ii+1;
Finally you have to change the while loop condition; while n(ii) == 1 means that the loops only continues if the n is 1, but it should continue if n is NOT 1.

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