Given a string of digits 0 – 9. The task is to count number of substrings which when convert into integer form an even number.
Input : str = "1234". Output : 6 "2", "4", "12", "34", "234", "1234" are 6 substring which are even. Input : str = "154". Output : 3 Input : str = "15". Output : 0
For a number to be even, substring must end wit an even digit. We find all the even digits in the string and for each even digit, count the number of substrings ending with it. Now, observe that the number of substrings will be index of that even digit plus one.
Time Complexity: O(length of string).
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