LeetCode1232. Check If It Is a Straight Line

一、题目

You are given an array coordinates, coordinates[i] = [x, y], where [x, y] represents the coordinate of a point. Check if these points make a straight line in the XY plane.

Example 1:

Input: coordinates = [[1,2],[2,3],[3,4],[4,5],[5,6],[6,7]]
Output: true
Example 2:

Input: coordinates = [[1,1],[2,2],[3,4],[4,5],[5,6],[7,7]]
Output: false

Constraints:

2 <= coordinates.length <= 1000
coordinates[i].length == 2
-10^4 <= coordinates[i][0], coordinates[i][1] <= 10^4
coordinates contains no duplicate point.

二、题解

class Solution {
public:
    bool checkStraightLine(vector<vector<int>>& coordinates) {
        int n = coordinates.size();
        double x1 = coordinates[0][0],x2 = coordinates[1][0];
        double y1 = coordinates[0][1],y2 = coordinates[1][1];
        if(x1 - x2 == 0){
            for(int i = 2;i < n;i++){
                if(coordinates[i][0] != x1) return false;
            }
            return true;
        }
        double k = (y2 - y1) / (x2 - x1);
        double b = y1 - k * x1;
        for(int i = 2;i < n;i++){
            double xi = coordinates[i][0],yi = coordinates[i][1];
            if(yi != k * xi + b) return false;
        }
        return true;
    }
};