# Number of Steps to Reduce a Number to Zero (via Leetcode)¶

Date published: 2020-03-27

Category: Python

Subcategory: Beginner Algorithms

Tags: functions, loops, modulo, dictionaries

This problem can be found on Leetcode.

Given a non-negative integer `num`

, return the number of steps to reduce it to zero. If the current number is even, divide it by 2; otherwise, subtract one from it.

### Write out Test Cases¶

```
# assert number_of_steps(8) == 4
```

To elaborate on test case above. Here are the steps:

`num`

of 8 is even; divide by 2;`num`

equals 4`num`

of 4 is even; divide by 2;`num`

equals 2`num`

of 2 is even; divide by 2;`num`

equals 1`num`

of 1 is odd; subtract 1;`num`

equals 0

```
# assert number_of_steps(14) == 6
```

To elaborate on test case above. Here are the steps:

`num`

of 14 is even; divide by 2;`num`

equals 7`num`

of 7 is odd; subtract 1;`num`

equals 6`num`

of 6 is even; divide by 2;`num`

equals 3`num`

of 3 is odd; subtract 1;`num`

equals 2`num`

of 2 is even; divide by 2;`num`

equals 1`num`

of 1 is odd; subtract 1;`num`

equals 0

### Pseudocode¶

```
# define function to take in num
# set a variable for count of steps
# while num is not equal to 0:
# if num is even:
# reassign num to be num divided by 2
# else:
# number is odd...
# reassign num to be num minus 1
# increment count of steps variable by 1
# return count of steps
```

My solution above is the simplest possible solution. I wouldn't worry about time or space complexity considerations here. Time complexity is *roughly* O(n/2) and space complexity is simply O(1) for the one variable created.

### Code¶

```
def number_of_steps(num):
count_of_steps = 0
while num != 0:
if num % 2 == 0:
num /= 2
else:
# number is odd...
num -= 1
count_of_steps += 1
return count_of_steps
```

### Verify test cases¶

```
assert number_of_steps(8) == 4
```

```
assert number_of_steps(14) == 6
```