Minimum Cost to Convert String I — LeetCode 2976 Python Solution

The problem

You are given two 0-indexed strings source and target, both of length n and consisting of lowercase English letters. You are also given two 0-indexed character arrays original and changed, and an integer array cost, where cost[i] represents the cost of changing the character original[i] to the character changed[i].

Example

Input

source = "abcd", target = "acbe", original = ["a","b","c","c","e","d"], changed = ["b","c","b","e","b","e"], cost = [2,5,5,1,2,20]

Output

28

Explanation

To convert the string "abcd" to string "acbe":

Python solution

class Solution:
    def minimumCost(
        self,
        source: str,
        target: str,
        original: List[str],
        changed: List[str],
        cost: List[int],
    ) -> int:
        g = [[inf] * 26 for _ in range(26)]
        for i in range(26):
            g[i][i] = 0
        for x, y, z in zip(original, changed, cost):
            x = ord(x) - ord('a')
            y = ord(y) - ord('a')
            g[x][y] = min(g[x][y], z)
        for k in range(26):
            for i in range(26):
                for j in range(26):
                    g[i][j] = min(g[i][j], g[i][k] + g[k][j])
        ans = 0
        for a, b in zip(source, target):
            if a != b:
                x, y = ord(a) - ord('a'), ord(b) - ord('a')
                if g[x][y] >= inf:
                    return -1
                ans += g[x][y]
        return ans

Complexity

Pattern: Depth-First Search

Follow one path to its end before trying the next — the default way to explore a graph. LeetCode 2976. Minimum Cost to Convert String I is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Graph.

The depth-first search guide has the Python template for the pattern and the 366 LeetCode problems that use it.

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