149. Max Points on a Line

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.

Example 1:

Input: [[1,1],[2,2],[3,3]]
Output: 3
Explanation:
^
|
|        o
|     o
|  o  
+------------->
0  1  2  3  4

Example 2:

Input: [[1,1],[3,2],[5,3],[4,1],[2,3],[1,4]]
Output: 4
Explanation:
^
|
|  o
|     o        o
|        o
|  o        o
+------------------->
0  1  2  3  4  5  6

NOTE: input types have been changed on April 15, 2019. Please reset to default code definition to get new method signature.

/**
 * @param {number[][]} points
 * @return {number}
 */
var maxPoints = function(points) {
    const len = points.length
    if (len <= 2) {
        return len
    }
    // 至少有两个点在一条直线上
    let count = 2
    // 存储相同点个数
    let same = 0
    for (let i = 0; i < len; i++) {
        const p1 = points[i]
        // 保存每一轮循环在一条直线上的最大点数量
        let max = 0
        // 用一个map来存储包括当前点最多可以有几个点同在直线
        const map = new Map()
        for (let j = 0; j < len; j++) {
            if (i != j) {
                const p2 = points[j]
                if (isSamePoint(p1, p2)) {
                    same ++
                } else {
                    const arg = getLinerfunction(p1, p2)
                    if (!map.has(arg)) {
                        map.set(arg, 2)
                    } else {
                        map.set(arg, map.get(arg) + 1)
                    }
                }                       
            }
        }
        map.forEach(arg => {
            max = Math.max(max, arg)
        })
        // 如果max为0，说明所有点都是相同点，则直接返回len
        if (max) {        
            max += same
        } else {
            return len
        }
        // 记得每次循环结束same归零，更新count
        same = 0
        count = Math.max(count, max)
    }
    return count
};

// 根据两点得到直线方程参数
function getLinerfunction (p1, p2) {
    // 防止数据越界，对数据做一个缩放
    const maxInt = 0xffffff
    const k = ((p1[1] - p2[1]) % maxInt * maxInt) / (p1[0] - p2[0])
    const b = p1[1] - k * p1[0]
    return `${k}+${b}`
}
// 判断两个点是否是同一个点
function isSamePoint (p1, p2) {
    return (p1[0] === p2[0]) && (p1[1] === p2[1])
}