LeetCode in Kotlin

2013. Detect Squares

Medium

You are given a stream of points on the X-Y plane. Design an algorithm that:

• Adds new points from the stream into a data structure. Duplicate points are allowed and should be treated as different points.
• Given a query point, counts the number of ways to choose three points from the data structure such that the three points and the query point form an axis-aligned square with positive area.

An axis-aligned square is a square whose edges are all the same length and are either parallel or perpendicular to the x-axis and y-axis.

Implement the DetectSquares class:

• DetectSquares() Initializes the object with an empty data structure.
• void add(int[] point) Adds a new point point = [x, y] to the data structure.
• int count(int[] point) Counts the number of ways to form axis-aligned squares with point point = [x, y] as described above.

Example 1:

Input [“DetectSquares”, “add”, “add”, “add”, “count”, “count”, “add”, “count”] [[], [[3, 10]], [[11, 2]], [[3, 2]], [[11, 10]], [[14, 8]], [[11, 2]], [[11, 10]]]

Output: [null, null, null, null, 1, 0, null, 2]

Explanation:

DetectSquares detectSquares = new DetectSquares();

detectSquares.add([3, 10]);

detectSquares.add([11, 2]);

detectSquares.add([3, 2]);

detectSquares.count([11, 10]); // return 1. You can choose: // - The first, second, and third points

detectSquares.count([14, 8]); // return 0. The query point cannot form a square with any points in the data structure.

detectSquares.add([11, 2]); // Adding duplicate points is allowed.

detectSquares.count([11, 10]); // return 2. You can choose: // - The first, second, and third points // - The first, third, and fourth points

Constraints:

• point.length == 2
• 0 <= x, y <= 1000
• At most 3000 calls in total will be made to add and count.

Solution

class DetectSquares {
    private val map: MutableMap<Int, IntArray>

    init {
        map = HashMap()
    }

    fun add(point: IntArray) {
        val x = point[0]
        val y = point[1]
        val hash = x * MUL + y
        if (map.containsKey(hash)) {
            map[hash]!![2]++
        } else {
            map[hash] = intArrayOf(x, y, 1)
        }
    }

    fun count(point: IntArray): Int {
        var ans = 0
        val x = point[0]
        val y = point[1]
        for ((_, diap) in map) {
            val x1 = diap[0]
            val y1 = diap[1]
            val num = diap[2]
            if (Math.abs(x - x1) == Math.abs(y - y1) && x != x1 && y != y1) {
                val p1hash = x * MUL + y1
                val p2hash = x1 * MUL + y
                if (map.containsKey(p1hash) && map.containsKey(p2hash)) {
                    ans += map[p1hash]!![2] * map[p2hash]!![2] * num
                }
            }
        }
        return ans
    }

    companion object {
        private const val MUL = 1002
    }
}
/*
 * Your DetectSquares object will be instantiated and called as such:
 * var obj = DetectSquares()
 * obj.add(point)
 * var param_2 = obj.count(point)
 */

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