1404. Number of Steps to Reduce a Number in Binary Representation to One
Medium
Given the binary representation of an integer as a string s, return the number of steps to reduce it to 1 under the following rules:
If the current number is even, you have to divide it by 2.
If the current number is odd, you have to add 1 to it.
It is guaranteed that you can always reach one for all test cases.
Example 1:
Input: “1101”
Output: 6
Explanation: “1101” corressponds to number 13 in their decimal representation.
Step 1) 13 is odd, add 1 and obtain 14.
Step 2) 14 is even, divide by 2 and obtain 7.
Step 3) 7 is odd, add 1 and obtain 8.
Step 4) 8 is even, divide by 2 and obtain 4.
Step 5) 4 is even, divide by 2 and obtain 2.
Step 6) 2 is even, divide by 2 and obtain 1.
Example 2:
Input: s = “10”
Output: 1
Explanation: “10” corressponds to number 2 in their decimal representation.
Step 1) 2 is even, divide by 2 and obtain 1.
Example 3:
Input: s = “1”
Output: 0
Constraints:
1 <= s.length <= 500
s consists of characters ‘0’ or ‘1’
s[0] == ‘1’
Solution:
/**
* @param String $s
* @return Integer
*/
function numSteps($s) {
$ans = 0;
while ($s[strlen($s) – 1] == ‘0’) {
$s = substr($s, 0, -1);
++$ans;
}
if ($s == “1”) return $ans;
++$ans;
for ($i = 0; $i < strlen($s); $i++) {
$ans += $s[$i] == ‘1’ ? 1 : 2;
}
return $ans;
}
}
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