LeetCode: Queens That Can Attack the King

Queens That Can Attack the King

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On an 8×8 chessboard, there can be multiple Black Queens and one White King.

Given an array of integer coordinates queens that represents the positions of the Black Queens, and a pair of coordinates king that represent the position of the White King, return the coordinates of all the queens (in any order) that can attack the King.

Example 1:

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 queen at [0,1] can attack the king cause they're in the same row. 
The queen at [1,0] can attack the king cause they're in the same column. 
The queen at [3,3] can attack the king cause they're in the same diagnal. 
The queen at [0,4] can't attack the king cause it's blocked by the queen at [0,1]. 
The queen at [4,0] can't attack the king cause it's blocked by the queen at [1,0]. 
The queen at [2,4] can't attack the king cause it's not in the same row/column/diagnal as the king.

Example 2:

Input: queens = [[0,0],[1,1],[2,2],[3,4],[3,5],[4,4],[4,5]], king = [3,3]
Output: [[2,2],[3,4],[4,4]]

Example 3:

Input: queens = [[5,6],[7,7],[2,1],[0,7],[1,6],[5,1],[3,7],[0,3],[4,0],[1,2],[6,3],[5,0],[0,4],[2,2],[1,1],[6,4],[5,4],[0,0],[2,6],[4,5],[5,2],[1,4],[7,5],[2,3],[0,5],[4,2],[1,0],[2,7],[0,1],[4,6],[6,1],[0,6],[4,3],[1,7]], king = [3,4]
Output: [[2,3],[1,4],[1,6],[3,7],[4,3],[5,4],[4,5]]

Constraints:

• 1 <= queens.length <= 63
• queens[0].length == 2
• 0 <= queens[i][j] < 8
• king.length == 2
• 0 <= king[0], king[1] < 8
• At most one piece is allowed in a cell.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

• Solution

// https://code.dennyzhang.com/queens-that-can-attack-the-king
// Basic Ideas: array
//
//   From King position, check all 8 directions. 
//   And stop when it hits a queen or the boundries
//
// Complexity: Time O(n), Space O(n)
func queensAttacktheKing(queens [][]int, king []int) [][]int {
    m := map[[2]int]bool{}
    for _, q := range queens {
        m[[2]int{q[0], q[1]}] = true
    }
    res := [][]int{}
    i, j := king[0], king[1]
    for x:=-1; x<=1; x++ {
        for y:=-1; y<=1; y++ {
            if x==0 && y==0 {
                continue
            }
            // keep searching this direction
            i2, j2 := i+x, j+y
            for i2>=0 && i2<8 && j2>=0 && j2<8 {
                if m[[2]int{i2,j2}] {
                    res = append(res, []int{i2, j2})
                    break
                }
                i2, j2 = i2+x, j2+y
            }
        }
    }
    return res
}