1865.js

/** ------------------------------------------------------------------------------
 * 
 * 1865. Finding Pairs With a Certain Sum
 * Topics: Array, Hash Table
 * https://leetcode.com/problems/finding-pairs-with-a-certain-sum/description/?envType=daily-question&envId=2025-07-06
 * 
 ------------------------------------------------------------------------------ */
/**
 * @param {number[]} nums1
 * @param {number[]} nums2
 */
var FindSumPairs = function (nums1, nums2) {
  this.nums1 = nums1
  this.nums2 = nums2
  this.map2 = new Map()

  for (const num of nums2) {
    this.map2.set(num, (this.map2.get(num) || 0) + 1)
  }
}

/**
 * @param {number} index
 * @param {number} val
 * @return {void}
 */
FindSumPairs.prototype.add = function (index, val) {
  const oldVal = this.nums2[index]
  this.map2.set(oldVal, this.map2.get(oldVal) - 1)

  this.nums2[index] += val
  const newVal = this.nums2[index]
  this.map2.set(newVal, (this.map2.get(newVal) || 0) + 1)
}

/**
 * @param {number} tot
 * @return {number}
 */
FindSumPairs.prototype.count = function (tot) {
  let count = 0

  for (let num1 of this.nums1) {
    let num2 = tot - num1
    if (this.map2.has(num2)) count += this.map2.get(num2)
  }

  return count
}

console.log(
  new FindSumPairs(
    ["FindSumPairs", "count", "add", "count", "count", "add", "add", "count"],
    [
      [1, 1, 2, 2, 2, 3],
      [1, 4, 5, 2, 5, 4],
    ],
  ),
)