Triangular Numbers Pattern | FooBar

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I m trying to create the below pattern using the below code

7
4 8
2 5 9
1 3 6 10

def createpattern(n=4,max_val=10):
    pattern = []
    for x in range(1,n+1):
        temp = []
        step = 2
        val = x
        bool_flag = 1
        while bool_flag == 1:
             temp += [val]
             if val == max_val:
                 print('----->')
                 bool_flag = 0
                 print('before break')
                 break
             else:
                val = val + step
                step += 1

        print('after break')
        print(temp)
        max_val = max_val - 1
        pattern.append(temp)

The break under while loop is working as expected

I m able to generate the first row however , the range in for loop is not moving to the next iteration value it is stuck at 1.

I have tried adding a continue at the end after append , however the loop is still stuck.

I m unable to figure out a way to rectify the above nested loop , ideally it should move to the next iteration value which I m unable to figure out why

Any leads would be helpful

while-loop for-loop algorithm python
3 Answers

When calling the function with the default arguments and looking at it in a debugger, on the second iteration it produces [2, 4, 7, 11, 16 ... and goes on forever. Because none of these values is equal to max_val, val == max_val is never true. After changing it to if val >= max_val:, I get the following output:

----->
before break
after break
[1, 3, 6, 10]
----->
before break
after break
[2, 4, 7, 11]
----->
before break
after break
[3, 5, 8]
----->
before break
after break
[4, 6, 9]
user_20653890

The loop gets stuck due to the if val == max_val condition and incorrect step calculations. When the second row is created, the initial value of step should be 3, not 2. The result currently produced is [2, 4, 7, 11, ...] and the loop never terminates, since there is never a 9 in the array. That applies to the rest of the rows as well.

user_134846770

I was able to resolve it, the approach that I was taking was very naive and had to research a bit on the patterns

Useful link for any pattern sequence formulae can be found here - here

Over the course the numbers in the required pattern tends to follow a trend and are a direct derivative of Triangular Numbers

Code Snippet -- 

def createpattern(x, y):
    pattern = []

    traingular_nums = [n*(n+1)/2 for n in range(1,y+x+1)]

    pattern.append(traingular_nums)

    for i in range(2,x+y+1):
        k = (i*(i-1)/2) + 1  <----- Formulae for Triangular Numbers
        temp = []
        temp.append(k)
        for z in range(1,len(pattern[i-2])-1):
            v = temp[z-1] + pattern[i-2][z+1] - pattern[i-2][z]
            temp.append(v)
        pattern.append(temp)
return pattern

The pattern was part of Google Foobar Challenge

user_91089120
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