LeetCode 1037. 有效的回旋镖

直接向量叉乘就可以，自己还判断了三条斜率；

class Solution {
public:
    bool isBoomerang(vector>& points) {
        double x1=points[0][0],x2=points[1][0],x3=points[2][0];
        double y1=points[0][1],y2=points[1][1],y3=points[2][1];
        double k1=x2-x1==0?INT_MAX:(y2-y1)/(x2-x1);
        double k2=x3-x1==0?INT_MAX:(y3-y1)/(x3-x1);
        double k3=x3-x2==0?INT_MAX:(y3-y2)/(x3-x2);
        if(k1!=k2&&k2!=k3&&k1!=k3)
            return true;
        return false;
    }
};

class Solution {
public:
    bool isBoomerang(vector>& points) {
        vector v1 = {points[1][0] - points[0][0], points[1][1] - points[0][1]};
        vector v2 = {points[2][0] - points[0][0], points[2][1] - points[0][1]};
        return v1[0] * v2[1] - v1[1] * v2[0] != 0;
    }
};