README.md

447. Number of Boomerangs

Given n points in the plane that are all pairwise distinct, a "boomerang" is a tuple of points (i, j, k) such that the distance between i and j equals the distance between i and k (the order of the tuple matters).

Find the number of boomerangs. You may assume that n will be at most 500 and coordinates of points are all in the range [-10000, 10000] (inclusive).

Example:

Input:
[[0,0],[1,0],[2,0]]
Output:
2
Explanation:
The two boomerangs are [[1,0],[0,0],[2,0]] and [[1,0],[2,0],[0,0]]

Solutions (Rust)

1. HashMap

use std::collections::HashMap;

impl Solution {
    pub fn number_of_boomerangs(points: Vec<Vec<i32>>) -> i32 {
        let mut len_cnt = HashMap::new();
        let mut ret = 0;

        for i in 0..points.len() {
            for j in 0..points.len() {
                let dx = points[i][0] - points[j][0];
                let dy = points[i][1] - points[j][1];
                *len_cnt.entry(dx * dx + dy * dy).or_insert(0) += 1;
            }

            ret += len_cnt.values().map(|v| v * (v - 1)).sum::<i32>();
            len_cnt.clear();
        }

        ret
    }
}