Formatted question description: https://leetcode.ca/all/1828.html

1828. Queries on Number of Points Inside a Circle

Level

Medium

Description

You are given an array points where points[i] = [x_i, y_i] is the coordinates of the i-th point on a 2D plane. Multiple points can have the same coordinates.

You are also given an array queries where queries[j] = [x_j, y_j, r_j] describes a circle centered at (x_j, y_j) with a radius of r_j.

For each query queries[j], compute the number of points inside the j-th circle. Points on the border of the circle are considered inside.

Return an array answer, where answer[j] is the answer to the j-th query.

Example 1:

Image text

Input: points = [[1,3],[3,3],[5,3],[2,2]], queries = [[2,3,1],[4,3,1],[1,1,2]]

Output: [3,2,2]

Explanation: The points and circles are shown above.

queries[0] is the green circle, queries[1] is the red circle, and queries[2] is the blue circle.

Example 2:

Image text

Input: points = [[1,1],[2,2],[3,3],[4,4],[5,5]], queries = [[1,2,2],[2,2,2],[4,3,2],[4,3,3]]

Output: [2,3,2,4]

Explanation: The points and circles are shown above.

queries[0] is green, queries[1] is red, queries[2] is blue, and queries[3] is purple.

Constraints:

  • 1 <= points.length <= 500
  • points[i].length == 2
  • 0 <= x_i, y_i <= 500
  • 1 <= queries.length <= 500
  • queries[j].length == 3
  • 0 <= x_j, y_j <= 500
  • 1 <= r_j <= 500
  • All coordinates are integers.

Solution

For each query, obtain the values x, y and r, and for each point, calculate the squared distance between the query’s center and the point. If the squared distance is less than or equal to r * r, then the point is inside the circle. The number of points inside each circle can be calculated.

class Solution {
    public int[] countPoints(int[][] points, int[][] queries) {
        int queriesCount = queries.length;
        int[] counts = new int[queriesCount];
        for (int i = 0; i < queriesCount; i++) {
            int[] query = queries[i];
            int x = query[0], y = query[1], r = query[2];
            int rSquare = r * r;
            for (int[] point : points) {
                int distanceSquare = getDistanceSquare(point, x, y);
                if (distanceSquare <= rSquare)
                    counts[i]++;
            }
        }
        return counts;
    }

    public int getDistanceSquare(int[] point, int x, int y) {
        return (x - point[0]) * (x - point[0]) + (y - point[1]) * (y - point[1]);
    }
}

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