Leetcode——回旋镖

Posted 2021-10-02 Yawn,

1. 回旋镖

（1）Hash表

class Solution {
    public int numberOfBoomerangs(int[][] points) {
        int len = points.length;
        int res = 0;

        for (int i = 0; i < len; i++) {
            Map<Integer, Integer> map = new HashMap<>();
            for (int j = 0; j < len; j++) {
                //剔除掉相同点
                if (i == j)
                    continue;
                int x = points[i][0] - points[j][0];
                int y = points[i][1] - points[j][1];
                //求距离， (x1 - x2)平方 - (y1 - y2)平方
                int dist = x*x + y*y; 
                map.put(dist, map.getOrDefault(dist, 0) + 1);
            }

            //统计回旋镖数量,逐次统计回旋镖数量
            for (int dist : map.keySet()) {
                int cnt = map.get(dist);
                res += cnt * (cnt - 1);
            }
        }

        return res;
    }
}