3623.js

/** ------------------------------------------------------------------------------
 * 
 * 3623. Count Number of Trapezoids I
 * Topics: Hash Table
 * https://leetcode.com/problems/count-number-of-trapezoids-i/description/?envType=daily-question&envId=2025-12-02
 * 
 ------------------------------------------------------------------------------ */
var countTrapezoids = function (points) {
  const pointNum = new Map()
  const mod = 1000000007n
  let ans = 0n,
    sum = 0n

  for (const point of points) {
    const y = point[1]
    pointNum.set(y, (pointNum.get(y) || 0) + 1)
  }

  for (const pNum of pointNum.values()) {
    const edge = (BigInt(pNum) * BigInt(pNum - 1)) / 2n
    ans = (ans + edge * sum) % mod
    sum = (sum + edge) % mod
  }

  return Number(ans)
}

console.log()