Find all the patterns of "1(0+)1" in a given string (General Approach)

A string contains patterns of the form 1(0+)1 where (0+) represents any non-empty consecutive sequence of 0's. Count all such patterns. The patterns are allowed to overlap.

Note : It contains digits and lowercase characters only. The string is not necessarily a binary. 100201 is not a valid pattern. 
One approach to solve the problem is discussed here, other using Regular expressions is given in Set 2 

Examples: 

Input : 1101001
Output : 2

Input : 100001abc101
Output : 2

Let size of input string be n. 

1. Iterate through index '0' to 'n-1'. 
2. If we encounter a '1', we iterate till the elements are '0'. 
3. After the stream of zeros ends, we check whether we encounter a '1' or not. 
4. Keep on doing this till we reach the end of string.

Below is the implementation of the above method. 

2

Time Complexity: O(n) 
Auxiliary Space: O(1)