447. Number of Boomerangs

题目

解题思路

对列表中每一个点p与其他点p计算距离，加入到一个字典d中。
根据d的结果，来判断形成回旋镖的排列组合数量。

代码

易读性与高效性并存的代码：

class Solution:
    def numberOfBoomerangs(self, points: 'List[List[int]]') -> 'int':
        i = 1
        c = 0
        for p1 in points:
            d = {}
            for p2 in points:
                x, y = p1[0]-p2[0], p1[1]-p2[1]
                distance = x*x + y*y
                if distance in d:
                    d[distance] += 1
                else:
                    d[distance] = 1
            for v in d.values():
                c += v*(v-1)
        return c

最简化代码：但不易读

class Solution:
    def numberOfBoomerangs(self, points):
        ans = 0
        for x1, y1 in points:
            cnts = {}
            for x2, y2 in points:
                dx = x1 - x2
                dy = y1 - y2
                d = dx * dx + dy * dy
                #将计算的部分 和统计合并
                if d in cnts:
                    ans += cnts[d]
                    cnts[d] += 1
                else:
                    cnts[d] = 1
        return 2 * ans