Robot Return to Origin — LeetCode 657 Python Solution

The problem

There is a robot starting at the position (0, 0), the origin, on a 2D plane. Given a sequence of its moves, judge if this robot ends up at (0, 0) after it completes its moves.

Example

Input

moves = "UD"

Output

true

Explanation

The robot moves up once, and then down once. All moves have the same magnitude, so it ended up at the origin where it started. Therefore, we return true.

Python solution

class Solution:
    def judgeCircle(self, moves: str) -> bool:
        x = y = 0
        for c in moves:
            match c:
                case "U":
                    y += 1
                case "D":
                    y -= 1
                case "L":
                    x -= 1
                case "R":
                    x += 1
        return x == 0 and y == 0

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 657. Robot Return to Origin is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

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

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