149-max-points-on-a-line.js

/**
 * @param {number[][]} points
 * @return {number}
 */
const maxPoints = function (points) {
  if (points.length < 2 || points == null) return points.length
  let max = 2
  for (let i = 0; i < points.length; i++) {
    let [p1x, p1y] = points[i]
    let samePoint = 1,
      map = { base: 0 } // to avoid when map = {}, the max value is -Infinity
    for (let j = i + 1; j < points.length; j++) {
      if (points[i][0] == points[j][0] && points[i][1] == points[j][1]) {
        samePoint++
      } else {
        let [p2x, p2y] = points[j]
        let slope = (1000000.0 * (p2y - p1y)) / (p2x - p1x)
        if (!Number.isFinite(slope)) slope = 'v'
        else if (Number.isNaN(slope)) slope = 'h'
        map[slope] = map[slope] + 1 || 1
      }
    }
    max = Math.max(Math.max(...Object.values(map)) + samePoint, max)
  }
  return max
}