JavaArithmetic/src/LeetCode/Leetcode447.java at master · freestylewill/JavaArithmetic · GitHub

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package LeetCode;

import java.util.HashMap;

public class Leetcode447 {

// 447. Number of Boomerangs

// https://leetcode.com/problems/number-of-boomerangs/description/

// 时间复杂度: O(n^2)

// 空间复杂度: O(n)

public int numberOfBoomerangs(int[][] points) {

int res = 0;

for( int i = 0 ; i < points.length ; i ++ ){

// record中存储点i 到所有其他点的距离出现的频次

HashMap<Integer, Integer> record = new HashMap<Integer, Integer>();

for(int j = 0 ; j < points.length ; j ++)

if(j != i){

// 计算距离时不进行开根运算, 以保证精度

int dis = dis(points[i], points[j]);

if(record.containsKey(dis))

record.put(dis, record.get(dis) + 1);

else

record.put(dis, 1);

}

for(Integer dis: record.keySet())

res += record.get(dis) * (record.get(dis) - 1);

}

return res;

}

// 两点之间的距离

private int dis(int[] pa, int pb[]){

return (pa[0] - pb[0]) * (pa[0] - pb[0]) +

(pa[1] - pb[1]) * (pa[1] - pb[1]);

}