Rings and Rods — LeetCode 2103 Python Solution

The problem

There are n rings and each ring is either red, green, or blue. The rings are distributed across ten rods labeled from 0 to 9.

Example

Input

rings = "B0B6G0R6R0R6G9"

Output

1

Explanation

- The rod labeled 0 holds 3 rings with all colors: red, green, and blue.

Python solution

class Solution:
    def countPoints(self, rings: str) -> int:
        mask = [0] * 10
        d = {"R": 1, "G": 2, "B": 4}
        for i in range(0, len(rings), 2):
            c = rings[i]
            j = int(rings[i + 1])
            mask[j] |= d[c]
        return mask.count(7)

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 2103. Rings and Rods is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Hash Table.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

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