Execution of All Suffix Instructions Staying in a Grid — LeetCode 2120 Python Solution

The problem

There is an n x n grid, with the top-left cell at (0, 0) and the bottom-right cell at (n - 1, n - 1). You are given the integer n and an integer array startPos where startPos = [startrow, startcol] indicates that a robot is initially at cell (startrow, startcol).

Example

Input

n = 3, startPos = [0,1], s = "RRDDLU"

Output

[1,5,4,3,1,0]

Explanation

Starting from startPos and beginning execution from the ith instruction:

Python solution

class Solution:
    def executeInstructions(self, n: int, startPos: List[int], s: str) -> List[int]:
        ans = []
        m = len(s)
        mp = {"L": [0, -1], "R": [0, 1], "U": [-1, 0], "D": [1, 0]}
        for i in range(m):
            x, y = startPos
            t = 0
            for j in range(i, m):
                a, b = mp[s[j]]
                if 0 <= x + a < n and 0 <= y + b < n:
                    x, y, t = x + a, y + b, t + 1
                else:
                    break
            ans.append(t)
        return ans

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 2120. Execution of All Suffix Instructions Staying in a Grid 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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