Python pattern looping

Question

I'm having trouble on printing alternate pattern, the output is suppose to look like this:

input height: 7

22
1122
221122
11221122
2211221122
112211221122
22112211221122

But instead it came out like this:

input height: 7
22
1111
222222
11111111
2222222222
111111111111
22222222222222

Code:

height = int (input ("input height: "))

for level in range (1, height+1):
    num = level

    for x in range (num):
        if( level%2==0): #Even row starts with "11" first
            print ("11",end = "")
        else:
            print ("22",end = "")
    print()

By using looping, while, for loop, no list. How can I do this?

2*level - level ? isn't that = level ?

njzk2
– njzk2

2013-09-24 15:25:24 +00:00
Commented Sep 24, 2013 at 15:25 — njzk2
– njzk2, Commented Sep 24, 2013 at 15:25

Marcin · Accepted Answer · 2013-09-24 15:26:49Z

2

It's not coming out like you want it, because you are choosing to use only one type of fill character per line with if(level%2==0):.

It looks like you need to figure out how to switch between two different fill values on each line. I suggest that:

You accumulate to a string for each line before printing
You look into how you can use a sequence (list or tuple) to cycle through values. There's also a tool in itertools you could use.

answered Sep 24, 2013 at 15:26

Marcin

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Comments

Steven Rumbalski · Accepted Answer · 2013-09-24 15:51:36Z

2

You could add to the string each iteration by inserting new characters from the left:

s = ""
for i in range(height):
    s = ('22', '11')[i % 2] + s
    print(s)

Or just build the whole string each iteration:

for i in range(height):
    print ''.join(('11', '22')[j % 2] for j in range(i + 1, 0, -1))

Or precompute the last row and slice it from the right:

s = '1122' * (height / 2 + 1)
for i in range(height):
    print s[(i+1) * -2:]

edited Sep 24, 2013 at 15:51

answered Sep 24, 2013 at 15:30

Steven Rumbalski

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Comments

Brian · Accepted Answer · 2013-09-24 15:27:58Z

1

For everything inside your x loop, level never changes. You need to alternate based on x while choosing your start based on level.

height = int (input ("input height: "))

for level in range (1, height+1):
    num = level

    for x in range (num):
        if( (level+x)%2==0): #Even row starts with "11" first
            print ("11",end = "")
        else:
            print ("22",end = "")
    print()

Notice how I add level and x before modding it against 2.

answered Sep 24, 2013 at 15:27

Brian

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1 Comment

Brian Over a year ago

@Chloe no problem. You were very close :)

Garth5689 · Accepted Answer · 2013-09-24 15:29:55Z

0

change:

if( level%2==0): #Even row starts with "11" first

to

if( (level+x) %2==0): #Even row starts with "11" first

Python 2.7:

for level in range(1,height+1):
     for x in range(level):                                                   
        if((level+x)%2==0):                                                  
            print "11",                                                      
        else:                                                                
            print "22",

answered Sep 24, 2013 at 15:29

Garth5689

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1 Comment

Garth5689 Over a year ago

edited, Brian beat me too it, and I forgot to alternate the start for x.

njzk2 · Accepted Answer · 2013-09-24 15:30:33Z

0

height = int (input ("input height: "))

for level in range (1, height+1):
   # Starting at level gives the proper oddity, while 2* level give the proper loop length
    for x in range (level, 2 * level):
        if( x%2==0): #Even row starts with "11" first
            print ("11",end="")
        else:
            print ("22",end="")
    print()

answered Sep 24, 2013 at 15:30

njzk2

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Comments

Dima Tisnek · Accepted Answer · 2013-09-24 15:35:48Z

0

tmp = "1122" * height
for tail in range(1, height+1):
    print tmp[-2*tail:]

done

answered Sep 24, 2013 at 15:35

Dima Tisnek

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