812. Largest Triangle Area

2023, Mar 29 2 mins read

1. Description

Given an array of points on the X-Y plane points where points[i] = [xi, yi], return the area of the largest triangle that can be formed by any three different points. Answers within 10-5 of the actual answer will be accepted.

2. Example

Example 1

Input: points = [[0,0],[0,1],[1,0],[0,2],[2,0]]
Output: 2.00000
Explanation: The five points are shown in the above figure. The red triangle is the largest.

Example 2

Input: points = [[1,0],[0,0],[0,1]]
Output: 0.50000

3. Constraints

3 <= points.length <= 50
-50 <= $x_i$, $y_i$ <= 50
All the given points are unique.

4. Solutions

Brute Force

n = points.size()
Time complexity: O($n^3$)
Space complexity: O(1)

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class Solution {
public:
    double largestTriangleArea(const vector<vector<int>>& points) {
        double result = 0;
        for (int i = 0; i < points.size() - 2; ++i) {
            for (int j = i + 1; j < points.size() - 1; ++j) {
                for (int k = j + 1; k < points.size(); ++k) {
                    int x1 = points[i][0], y1 = points[i][1];
                    int x2 = points[j][0], y2 = points[j][1];
                    int x3 = points[k][0], y3 = points[k][1];
                    result = max(result, 0.5 * abs(x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)));
                }
            }
        }

        return result;
    }
};

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