• 大数相加

const add = (a, b) => {
  const maxLength = Math.max(a.length, b.length)
  let overflow = false
  let sum = ''
  for(let i = 1; i <= maxLength; i++){
    const ai = a[a.length-i] || '0'
    const bi = b[b.length-i] || '0'
    let ci = parseInt(ai) + parseInt(bi) + overflow ? 1 : 0
    overflow = ci >= 10
    ci = overflow ? ci - 10 : ci
    sum = ci + sum 
  }
  sum = overflow ? '1' + sum : sum
  return sum
}

console.log(add("11111111101234567","77777777707654321"))
console.log(add("911111111101234567","77777777707654321"))

• or 15位加速版

const add = (a, b) => {
  const maxLength = Math.max(a.length, b.length)
  let overflow = false
  let sum = ''
  for(let i = 0; i < maxLength; i+=15){
    const ai = a.substring(a.length-i -15, a.length-i) || '0'
    const bi = b.substring(b.length-i -15, b.length-i) || '0'
    let ci = parseInt(ai) + parseInt(bi)
    overflow = ci > 999999999999999 // 15 个 9
    ci = overflow ? ci - (999999999999999+1) : ci
    sum = ci + sum 
  }
  sum = overflow ? '1' + sum : sum
  return sum
}

console.log(add("11111111101234567","77777777707654321"))
console.log(add("911111111101234567","77777777707654321"))

• 两数之和

const numbers = [2,7,11,15]
const target = 9
const twoSum = (numbers, target) => {
  const map = {}
  for(let i = 0; i < numbers.length; i++){
    const number = numbers[i]
    const number2 = target - number
    if(number2 in map){
      const number2Index = map[number2]
      return [i, number2Index]
    } else {
      map[number] = i
    }
  }
  return []
}
console.log(twoSum(numbers, target))

• 无重复最长子串的长度

• V1

var lengthOfLongestSubstring = function(s) {
  if (s.length <= 1)
    return s.length
  let max = 0
  let p1 = 0
  let p2 = 1
  const map = {}
  map[s[p1]] = 0
  while (p2 < s.length) {
    let hasSame = false
    if(s[p2] in map){
      hasSame = true
      if(map[s[p2]] >= p1){
          p1 = map[s[p2]] + 1
      }
    }
    map[s[p2]] = p2
    let tempMax = p2 - p1 + 1
    if(tempMax > max) max = tempMax
    p2 += 1
  }
  return max
};

• V2

var lengthOfLongestSubstring = function(s) {
  if (s.length <= 1)
    return s.length
  let max = 0
  let p1 = 0
  let p2 = 1
  const map = new Map()
  map.set(s[p1], 0)
  while (p2 < s.length) {
    let hasSame = false
    if(map.has(s[p2])){
      hasSame = true
      if(map.get(s[p2]) >= p1){
          p1 = map.get(s[p2]) + 1
      }
    }
    map.set(s[p2],p2)
    let tempMax = p2 - p1 + 1
    if(tempMax > max) max = tempMax
    p2 += 1
  }
  return max
};