# Avoid using double as key by a custom hasher

• I just found that in my previous submission I used unordered_map<double, int> in which the key is the slope of lines. I think comparing double for equality is bad practice so I write a Line class and use it as the key. To be able to use Line as key I overwrite the operator== in the Line class and I write a custom hasher for the Line class. Here is the code.

``````struct Line {
Line(const Point& a, const Point& b, double eps=1e-7) {
epsilon = eps;
isSamePoint = false;
isSlopeVertical = false;
slope = 0;

if(a.x == b.x && a.y==b.y) isSamePoint = true;
else if(a.x == b.x) isSlopeVertical = true;
else slope = double(a.y-b.y)/double(a.x-b.x);
}

bool operator==(const Line& other) const {
return fabs(slope-other.slope) < epsilon;
}

double epsilon;
double slope;
bool isSlopeVertical;
bool isSamePoint;
};

struct LineHasher {
size_t operator()(const Line& l) const {
return hash<double>()(l.slope);
}
};

class Solution {
public:
int maxPoints(vector<Point> &points) {
if(points.size() <= 2) return points.size();

int globalMax = 0;
for(int i=0; i<points.size()-1; i++) {
unordered_map<Line,int,LineHasher> map;
int samePoint = 0, vertical = 0, localMax = 0;
for(int j=i+1; j<points.size(); j++) {
Line l(points[i],points[j]);
if(l.isSamePoint) samePoint++;
else if(l.isSlopeVertical) vertical++;
else {
map[l]++;
localMax = max(localMax,map[l]);
}
}
localMax = max(localMax,vertical);
localMax += (samePoint + 1);
globalMax = max(globalMax,localMax);
}
return globalMax;
}
};``````

Looks like your connection to LeetCode Discuss was lost, please wait while we try to reconnect.