LeetCode No.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]]

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題目鏈接：https://leetcode.com/problems/number-of-boomerangs/

題目大意：求滿足條件的三元組個數。

思路：遍歷，用unordered_map統計所有點與points[i]的距離，ans += count * (count-1)

參考代碼：

class Solution {
public:
    int numberOfBoomerangs(vector<pair<int, int>>& points) {
        int n = points.size() , ans = 0 ;
        if ( n <= 2 )
            return 0 ;
        for ( int i = 0 ; i < n ; i ++ )
        {
            unordered_map <int,int> maping ;
            for ( int j = 0 ; j < n ; j ++ )
            {
                if ( i != j )
                    maping[getDis(points[i],points[j])] ++ ;
            }
            for ( auto& x : maping )
            {
                int count = x.second ;
                if ( count >= 2 )
                    ans += count * ( count - 1 ) ;
            }
        }
        return ans ;
    }
private:
    int getDis ( const pair <int,int>& a , const pair <int,int>& b )
    {
        return pow( ( a.first - b.first ) , 2 ) +  pow( ( a.second - b.second ) , 2 ) ;
    }
};