Minimum Operations to Make a Special Number — LeetCode 2844 Python Solution

The problem

You are given a 0-indexed string num representing a non-negative integer. In one operation, you can pick any digit of num and delete it.

Example

Input

num = "2245047"

Output

2

Explanation

Delete digits num[5] and num[6]. The resulting number is "22450" which is special since it is divisible by 25.

Python solution

class Solution:
    def minimumOperations(self, num: str) -> int:
        @cache
        def dfs(i: int, k: int) -> int:
            if i == n:
                return 0 if k == 0 else n
            ans = dfs(i + 1, k) + 1
            ans = min(ans, dfs(i + 1, (k * 10 + int(num[i])) % 25))
            return ans

        n = len(num)
        return dfs(0, 0)

Complexity

Pattern: Greedy

Take the locally best option every time — when you can prove that never costs you later. LeetCode 2844. Minimum Operations to Make a Special Number is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Greedy.

The greedy guide has the Python template for the pattern and the 346 LeetCode problems that use it.

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