2976. Minimum Cost to Convert String I - LeetCode

from typing import cast


class Solution:
    def minimumCost(
        self,
        source: str,
        target: str,
        original: list[str],
        changed: list[str],
        cost: list[int],
    ) -> int:
        BASE = ord('a')

        def to_i(a: str) -> int:
            return ord(a) - BASE

        MAX = float('inf')

        m = [[MAX for _ in range(26)] for _ in range(26)]  # mapping

        for s, t, c in zip(
            map(to_i, original),
            map(to_i, changed),
            cost,
        ):
            current_val = m[s][t]
            m[s][t] = min(current_val, c)

        for k in range(26):
            for i in range(26):
                for j in range(26):
                    another_path = m[i][k] + m[k][j]
                    m[i][j] = min(m[i][j], another_path)

        result = 0
        for s, t in zip(
            map(to_i, source),
            map(to_i, target),
        ):
            is_same = s == t
            distance = 0 if is_same else m[s][t]
            if distance == MAX:
                return -1
            result += cast(int, distance)
        return result