getPeakUserCount

peak.js

function swap (array, a, b) {
  var temp = array[a]
  array[b] = (array[a] = array[b], temp)
}

function makeSortedArray(x, y) {
  var sorted = []
  for (var i = x; i < y; ++i) sorted.push(i)
  return sorted
}

function makeUnsortedArray(a) {
  var arrayCopy = a.slice() // copy
  var currentIndex = arrayCopy.length

  while (currentIndex) {
    var randomIndex = Math.floor(Math.random() * currentIndex)
    swap(arrayCopy, --currentIndex, randomIndex)
  }

  return arrayCopy
}

function mergeArrays(a1, a2) {
  var merged = []
  var val1, val2;

  while (a1.length && a2.length) {
    if (val1 < val2){
      merged.push([val1, val2])
    }

    val1 = a1.pop()
    val2 = a2.pop()
  }

  return merged
}

var sortedStart = makeSortedArray(1, 700)
var sortedEnd = makeSortedArray(400, 1000)
var unsortedStart = makeUnsortedArray(sortedStart)
var unsortedEnd = makeUnsortedArray(sortedEnd)
var merged = mergeArrays(unsortedStart, unsortedEnd)
console.log('`merged` length', merged.length)
var data = [[1,10],[5,9],[7,13],[2,3],[15,20]]

function getPeakUserCount(a) {
  var map = {}
  a.forEach((time) => {
    for (var i = time[0]; i <= time[1]; ++i) {
      if (!map[i]) map[i] = 1
      else ++map[i]
    }
  })

  var largest = 0
  Object.keys(map).forEach((key) => {
    if (largest < map[key]) largest = map[key]
  })

  return largest
}

console.log(getPeakUserCount(data))
console.log(getPeakUserCount(merged))

function getPeakUserCount2(a) {
  var peak = a.reduce((accum, point) => {
    if (!accum.hasOwnProperty(point[0])) {
      accum[point[0]] = 0;
    }
    if (!accum.hasOwnProperty(point[1])) {
      accum[point[1]] = 0;
    }
    accum[point[0]]++;
    accum[point[1]]--;
    return accum;
  }, {});

  var max = 0;
  var current = 0;
  for (var time in peak) {
    current += peak[time]
    if (current > max) {
      max = current;
    }
  }

  return max
}

console.log(getPeakUserCount2(data))
console.log(getPeakUserCount2(merged))