Queens That Can Attack the King — LeetCode 1222 Python Solution

The problem

On a 0-indexed 8 x 8 chessboard, there can be multiple black queens and one white king. You are given a 2D integer array queens where queens[i] = [xQueeni, yQueeni] represents the position of the ith black queen on the chessboard.

Example

Input

queens = [[0,1],[1,0],[4,0],[0,4],[3,3],[2,4]], king = [0,0]

Output

[[0,1],[1,0],[3,3]]

Explanation

The diagram above shows the three queens that can directly attack the king and the three queens that cannot attack the king (i.e., marked with red dashes).

Python solution

class Solution:
    def queensAttacktheKing(
        self, queens: List[List[int]], king: List[int]
    ) -> List[List[int]]:
        n = 8
        s = {(i, j) for i, j in queens}
        ans = []
        for a in range(-1, 2):
            for b in range(-1, 2):
                if a or b:
                    x, y = king
                    while 0 <= x + a < n and 0 <= y + b < n:
                        x, y = x + a, y + b
                        if (x, y) in s:
                            ans.append([x, y])
                            break
        return ans

Complexity

Pattern: Matrix and Grid

Treat a 2-D grid as a graph whose neighbours are the four adjacent cells. LeetCode 1222. Queens That Can Attack the King is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Matrix.

The matrix and grid guide has the Python template for the pattern and the 216 LeetCode problems that use it.

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