num_steps_reduce_to_zero.cpp

/*
    Given an integer num, return the number of steps to reduce it to zero.

    In one step, if the current number is even, you have to divide it by 2, otherwise, you have to subtract 1 from it.

    Example 1:
    Input: num = 14
    Output: 6
    Explanation: 
    Step 1) 14 is even; divide by 2 and obtain 7. 
    Step 2) 7 is odd; subtract 1 and obtain 6.
    Step 3) 6 is even; divide by 2 and obtain 3. 
    Step 4) 3 is odd; subtract 1 and obtain 2. 
    Step 5) 2 is even; divide by 2 and obtain 1. 
    Step 6) 1 is odd; subtract 1 and obtain 0.
    
    Example 2:
    Input: num = 8
    Output: 4
    Explanation: 
    Step 1) 8 is even; divide by 2 and obtain 4. 
    Step 2) 4 is even; divide by 2 and obtain 2. 
    Step 3) 2 is even; divide by 2 and obtain 1. 
    Step 4) 1 is odd; subtract 1 and obtain 0.
    
    Example 3:
    Input: num = 123
    Output: 12

    Constraints: 0 <= num <= 106
*/
class Solution {
public:
    int numberOfSteps(int num) {
        // We initialize the step counter.
        int steps = 0;
        // While the number is still not zero...
        while (num != 0) {
            // ...we check if it is odd or even.
            // If it is even...
            if (num % 2 == 0) {
                // ...we divide it by 2 and increase the step counter.
                num /= 2;
                steps++;
            // If it is odd...
            } else {
                // ...we substract 1 and increase the step counter.
                num -= 1;
                steps++;
            }
        }
        // Finally, we return the step counter.
        return steps;
    }
};