Double Modular Exponentiation — LeetCode 2961 Python Solution

The problem

You are given a 0-indexed 2D array variables where variables[i] = [ai, bi, ci, mi], and an integer target. An index i is good if the following formula holds: 0 <= i < variables.length ((aibi % 10)ci) % mi == target Return an array consisting of good indices in any order.

Example

Input

variables = [[2,3,3,10],[3,3,3,1],[6,1,1,4]], target = 2

Output

[0,2]

Explanation

For each index i in the variables array:

Python solution

class Solution:
    def getGoodIndices(self, variables: List[List[int]], target: int) -> List[int]:
        return [
            i
            for i, (a, b, c, m) in enumerate(variables)
            if pow(pow(a, b, 10), c, m) == target
        ]

Complexity

Pattern: Math and Number Theory

Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 2961. Double Modular Exponentiation is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math.

The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.

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