[LeetCode] Challenge log 796

Posted on | Edited on |
797. Rotate String

Use hash function to compare if B is a “rotate string” of A

We are given two strings, A and B.

A shift on A consists of taking string A and moving the leftmost character to the rightmost position. For example, if A = 'abcde', then it will be 'bcdea' after one shift on A. Return True if and only if A can become B after some number of shifts on A.

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Example 1:
Input: A = 'abcde', B = 'cdeab'
Output: true

Example 2:
Input: A = 'abcde', B = 'abced'
Output: false

Note:

  • A and B will have length at most 100.
Soulution:
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class Solution:
    def rotateString(self, A, B):
        """
        :type A: str
        :type B: str
        :rtype: bool
        """
        if A == '' and B == '': return True
        A2 = A + A
        n = len(A)
        shift = set()
        for i in range(n):
            shift.add(A2[i:i + n])
            if B in shift: 
                return True
            else:
                shift.remove(A2[i:i + n])
        return False
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