Count Words Obtained After Adding a Letter — LeetCode 2135 Python Solution

The problem

You are given two 0-indexed arrays of strings startWords and targetWords. Each string consists of lowercase English letters only.

Example

Input

startWords = ["ant","act","tack"], targetWords = ["tack","act","acti"]

Output

2

Explanation

- In order to form targetWords[0] = "tack", we use startWords[1] = "act", append 'k' to it, and rearrange "actk" to "tack".

Python solution

class Solution:
    def wordCount(self, startWords: List[str], targetWords: List[str]) -> int:
        s = {sum(1 << (ord(c) - 97) for c in w) for w in startWords}
        ans = 0
        for w in targetWords:
            x = sum(1 << (ord(c) - 97) for c in w)
            for c in w:
                if x ^ (1 << (ord(c) - 97)) in s:
                    ans += 1
                    break
        return ans

Complexity

Pattern: Bit Manipulation

Use XOR, masks and the low-bit trick to replace whole data structures with an integer. LeetCode 2135. Count Words Obtained After Adding a Letter is filed here because LeetCode tags it Bit Manipulation, which is the vocabulary this hub collects.

The bit manipulation guide has the Python template for the pattern and the 194 LeetCode problems that use it.

Related problems