problem

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

submission

// we don't actually need to simulate this
// example: 0b00101010
// 2 ops to remove a 1 from this binary
// 1 op to remove a 0 (only the 0s after the first 1)
// with leading_zeros, we have
// steps = 2 * count1 + count0 - 1
//       = 64 + leading_zeros - count_zeros - 1
impl Solution {
    pub fn number_of_steps(num: i32) -> i32 {
        (match num {
            0 => 0, // special case 0
            num => 64 - num.leading_zeros() - num.count_zeros() - 1,
        }) as _
    }
}