Unique Substrings in Wraparound String — LeetCode 467 Python Solution

The problem

We define the string base to be the infinite wraparound string of "abcdefghijklmnopqrstuvwxyz", so base will look like this: "...zabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcd....". Given a string s, return the number of unique non-empty substrings of s are present in base.

Example

Input

s = "a"

Output

1

Explanation

Only the substring "a" of s is in base.

Python solution

class Solution:
    def findSubstringInWraproundString(self, s: str) -> int:
        f = defaultdict(int)
        k = 0
        for i, c in enumerate(s):
            if i and (ord(c) - ord(s[i - 1])) % 26 == 1:
                k += 1
            else:
                k = 1
            f[c] = max(f[c], k)
        return sum(f.values())

Complexity

Pattern: Dynamic Programming

Define a state, write the transition, and stop recomputing the same subproblem. LeetCode 467. Unique Substrings in Wraparound String is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Dynamic Programming.

The dynamic programming guide has the Python template for the pattern and the 481 LeetCode problems that use it.

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