写一个方法检测指定的数组是否有重复的元素

Answer 1

1. 不需要知道重复元素是什么

const isPureArray = array => {
  return [...new Set(array)].length === array.length
}
console.info(isPureArray([1, 2, 3, 4])) // true
console.info(isPureArray([1, 2, 3, 2])) // false

2. 需要知道重复元素的索引，这种情况下还需要考虑多次重复的情况

const getRepeatedItems = array => {
  const pureArray = [...new Set(array)]
  const repeatedItems = new Map()
  if (pureArray.length === array.length) return repeatedItems
  pureArray.forEach(item => {
    repeatedItems.set(item, [])
  })
  array.forEach((item, index) => {
    repeatedItems.get(item).push(index)
  });
  [...repeatedItems.keys()].forEach(key => {
    if (repeatedItems.get(key).length < 2) repeatedItems.delete(key)
  })
  return repeatedItems
}
const result = getRepeatedItems([1, 2, 3, 4, 1, 3, 4, 4, 2, 1, 1, 1, 5, 7])
// 然后就可以获取 result 内容，重复元素及其对应的每个重复索引