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Program to find number of substrings with only 1s using Python

Suppose we have a binary string s. We have to find the number of substrings with all characters 1's. The answer may be very large so return result mod 10^9 + 7.

So, if the input is like s = "1011010", then the output will be 5 because 1. four times "1" 2. one time "11"

To solve this, we will follow these steps −

  • m := 10^9+7

  • result := 0

  • div := divide the binary string by splitting it using '0'

  • for each x in div, do

    • if x is empty, then go for next iteration

    • result := result + quotient of (size of x *(size of x +1))/2

  • return result mod m

Let us see the following implementation to get better understanding −

Example

def solve(s):
   m = 10**9+7
   result = 0
   for x in s.split('0'):
      if not x: continue
      result += (len(x)*(len(x)+1)) // 2
   return result % m
s = "1011010"
print(solve(s))

Input

"1011010"

Output

5