Given a non-negative integer num, return the number of steps to reduce it to zero. 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 <= 10^6
class Solution {
public:
int numberOfSteps (int num) {
int res = 0;
#if 0
//The First solution
if (!num) return 0;
while (num)
{
if (num % 2 == 0)
num /= 2;
else
num -= 1;
res++;
}
#else
//Optimization
if (!num) return 0;
while (num)
{
res += (num & 1) ? 2 : 1;
num >>= 1;
}
#endif
return res-1;
}
};
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