Cinte's Leetcode Record
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149. 直线上最多的点数

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149. 直线上最多的点数

暴力 枚举斜率
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class Solution {
public:
    int maxPoints(vector<vector<int>>& points) {
        int sz = points.size();
        int ret = 1;
        for(int i = 0; i < sz; ++i)
        {
            unordered_map<double, int> map;
            for(int j = 0; j < sz; ++j)
            {
                if(j == i)
                    continue;
                double grad = (points[i][1] - points[j][1]) * 1.0/ (points[i][0] - points[j][0]); // 浮点除以0是不确定行为，不应该保留
                ++map[grad];
                ret = max(map[grad] + 1, ret);
            }
        }
        return ret;
    }
};
直接参考答案
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class Solution {
public:
    int maxPoints(vector<vector<int>>& points) {
        int sz = points.size();
        if(sz <= 2)
            return sz;
        int ret = 0;
        for(int i = 0; i < sz; ++i)
        {
            // 优化方案
            // 剩下的点都不如ret多了，那接下来不管怎么弄都超不过ret了，所以没用了意义
            if(ret > sz - i || ret > sz / 2)
                break;
            // 答案中的数字太抽象，这里将二元组用string表示
            unordered_map<string, int> map;
            for(int j = i + 1; j < sz; ++j)
            {
                int x = points[j][0] - points[i][0];
                int y = points[j][1] - points[i][1];
                if(x == 0)
                    y = 1;
                else if(y == 0)
                    x = 1;
                else
                {
                    if(y < 0)
                    {
                        x = -x;
                        y = -y;
                    }
                    int gcdXY = gcd(abs(x), abs(y));
                    x /= gcdXY;
                    y /= gcdXY;
                }
                ++map[to_string(x) + ":" + to_string(y)];
            }
            int maxN = 0;
            for(auto& [_, num] : map)
                maxN = max(maxN, num + 1);
            ret = max(ret, maxN);
        }
        return ret;
    }
private:
    // 欧几里得算法求公约数
    int gcd(int a, int b)
    {
        return b ? gcd(b, a % b) : a; 
    }
};