Given a string of 0 and 1, we need to check that the given string is valid or not. The given string is valid when there is no zero is present in between 1’s. For example, 1111, 0000111110, 1111000 are valid strings but 01010011, 01010, 101 are not.
One approach to solving the problem is discussed here, other using Regular expressions is given Set 2
Input : 100 Output : VALID Input : 1110001 Output : NOT VALID There is 0 between 1s Input : 00011 Output : VALID
- Find the first occurrence of 1 in the string. Let it be first.
- Find the last occurrence of 1 in the string. Let it be last.
- Run a loop from first to last and return false if there is a 0. If no 0 found, return true.
Explanation: Suppose we have a string: 01111011110000 Now take two variables say A and B. run a loop for 0 to length of the string and point A to the first occurrence of 1, after that again run a loop from length of the string to 0 and point second variable to the last occurrence of 1. So A = 1 (Position of first '1' is the string) and B = 9 (last occurrence of '1'). Now run a loop from A to B and check that '0' is present between 1 or not, if "YES" than set flag to 1 and break the loop, else set flag to 0. In this case flag will set to 1 as the given string is not valid and print "NOT VALID".
Time Complexity: O(n)
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