Count lattice points inside a circle

Array Hash Table Math Geometry Enumeration

56.5% acceptance

Feb 25, 2026

253

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Given a 2D integer array circles where circles[i] = [xi, yi, ri] represents the center (xi, yi) and radius ri of the ith circle drawn on a grid, return the number of lattice points that are present inside at least one circle. Note: A lattice point is a point with integer coordinates. Points that lie on the circumference of a circle are also considered to be inside it.

Solution

Rust

Time O(n³)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn count_lattice_points(circles: Vec<Vec<i32>>) -> i32 {
    use std::collections::HashSet;
    let mut points: HashSet<(i32, i32)> = HashSet::new();
    for c in &circles {
      let (cx, cy, r) = (c[0], c[1], c[2]);
      for x in (cx - r)..=(cx + r) {
        let dx = x - cx;
        let max_dy = ((r * r - dx * dx) as f64).sqrt() as i32;
        for y in (cy - max_dy)..=(cy + max_dy) {
          points.insert((x, y));
        }
      }
    }
    points.len() as i32
  }
}