812.最大三角形面积

链接：812.最大三角形面积
难度：Easy
标签：几何、数组、数学
简介：给定包含多个点的集合，从其中取三个点组成三角形，返回能组成的最大三角形的面积。

题解 1 - cpp

• 编辑时间：2022-03-20
• 执行用时：24ms
• 内存消耗：7.4MB
• 编程语言：cpp
• 解法介绍：遍历。

class Solution {
   public:
    double largestTriangleArea(vector<vector<int>>& points) {
        int n = points.size();
        double ans = 0;
        for (int i1 = 0; i1 < n; i1++) {
            for (int i2 = i1 + 1; i2 < n; i2++) {
                for (int i3 = i2 + 1; i3 < n; i3++) {
                    if (check(points, i1, i2, i3)) continue;
                    ans = max(ans, comp_area(points, i1, i2, i3));
                }
            }
        }
        return ans;
    }
    bool check(vector<vector<int>>& points, int i1, int i2, int i3) {
        return points[i1][0] == points[i2][0] &&
                   points[i1][0] == points[i3][0] ||
               points[i1][1] == points[i2][1] && points[i1][1] == points[i3][1];
    }
    double comp_area(vector<vector<int>>& points, int i1, int i2, int i3) {
        double line1 = comp_line(points, i1, i2),
               line2 = comp_line(points, i1, i3),
               line3 = comp_line(points, i2, i3),
               p = (line1 + line2 + line3) / 2;
        return sqrt(p * (p - line1) * (p - line2) * (p - line3));
    }
    double comp_line(vector<vector<int>>& points, int i1, int i2) {
        double x = pow(points[i1][0] - points[i2][0], 2),
               y = pow(points[i1][1] - points[i2][1], 2);
        return sqrt(x + y);
    }
};