2222 - Number of Ways to Select Buildings\.

Medium

You are given a 0-indexed binary string s which represents the types of buildings along a street where:

• s[i] = '0' denotes that the <code>i^th</code> building is an office and

• s[i] = '1' denotes that the <code>i^th</code> building is a restaurant.

As a city official, you would like to select 3 buildings for random inspection. However, to ensure variety, no two consecutive buildings out of the selected buildings can be of the same type.

• For example, given s = "0**0**1**1**0**1**", we cannot select the <code>1^st</code>, <code>3^rd</code>, and <code>5^th</code> buildings as that would form "0**11**" which is not allowed due to having two consecutive buildings of the same type.

Return the number of valid ways to select 3 buildings.

Example 1:

Input: s = "001101"

Output: 6

Explanation: The following sets of indices selected are valid:

• 0,2,4 from "001101" forms "010"

• 0,3,4 from "001101" forms "010"

• 1,2,4 from "001101" forms "010"

• 1,3,4 from "001101" forms "010"

• 2,4,5 from "001101" forms "101"

• 3,4,5 from "001101" forms "101"

No other selection is valid. Thus, there are 6 total ways.

Example 2:

Input: s = "11100"

Output: 0

Explanation: It can be shown that there are no valid selections.

Constraints:

• <code>3 <= s.length <= 10⁵</code>

• s[i] is either '0' or '1'.