LeetCode in Kotlin

497. Random Point in Non-overlapping Rectangles

Medium

You are given an array of non-overlapping axis-aligned rectangles rects where rects[i] = [ai, bi, xi, yi] indicates that (ai, bi) is the bottom-left corner point of the ith rectangle and (xi, yi) is the top-right corner point of the ith rectangle. Design an algorithm to pick a random integer point inside the space covered by one of the given rectangles. A point on the perimeter of a rectangle is included in the space covered by the rectangle.

Any integer point inside the space covered by one of the given rectangles should be equally likely to be returned.

Note that an integer point is a point that has integer coordinates.

Implement the Solution class:

• Solution(int[][] rects) Initializes the object with the given rectangles rects.
• int[] pick() Returns a random integer point [u, v] inside the space covered by one of the given rectangles.

Example 1:

Input [“Solution”, “pick”, “pick”, “pick”, “pick”, “pick”] [[[[-2, -2, 1, 1], [2, 2, 4, 6]]], [], [], [], [], []]

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

Explanation:

Solution solution = new Solution([[-2, -2, 1, 1], [2, 2, 4, 6]]);
solution.pick(); // return [1, -2]
solution.pick(); // return [1, -1]
solution.pick(); // return [-1, -2]
solution.pick(); // return [-2, -2]
solution.pick(); // return [0, 0]

Constraints:

• 1 <= rects.length <= 100
• rects[i].length == 4
• -109 <= ai < xi <= 109
• -109 <= bi < yi <= 109
• xi - ai <= 2000
• yi - bi <= 2000
• All the rectangles do not overlap.
• At most 104 calls will be made to pick.

Solution

import java.util.Random

@Suppress("kotlin:S2245")
class Solution(rects: Array<IntArray>) {
    private val weights: IntArray
    private val rects: Array<IntArray>
    private val random: Random

    init {
        weights = IntArray(rects.size)
        this.rects = rects
        random = Random()
        for (i in rects.indices) {
            val rect = rects[i]
            val count = (1 + rect[2] - rect[0]) * (1 + rect[3] - rect[1])
            weights[i] = (if (i == 0) 0 else weights[i - 1]) + count
        }
    }

    fun pick(): IntArray {
        val picked: Int = 1 + random.nextInt(weights[weights.size - 1])
        val idx = findGreaterOrEqual(picked)
        return getRandomPoint(idx)
    }

    private fun findGreaterOrEqual(target: Int): Int {
        var left = 0
        var right = weights.size - 1
        while (left + 1 < right) {
            val mid = left + (right - left) / 2
            if (weights[mid] >= target) {
                right = mid
            } else {
                left = mid + 1
            }
        }
        return if (weights[left] >= target) left else right
    }

    private fun getRandomPoint(idx: Int): IntArray {
        val r = rects[idx]
        val left = r[0]
        val right = r[2]
        val bot = r[1]
        val top = r[3]
        return intArrayOf(
            left + random.nextInt(right - left + 1), bot + random.nextInt(top - bot + 1)
        )
    }
}

/*
 * Your Solution object will be instantiated and called as such:
 * var obj = Solution(rects)
 * var param_1 = obj.pick()
 */

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