9.移除元素

var removeElement = (nums, val) => {
  let index = 0
  for (let i = 0; i < nums.length; i++) {
    if (nums[i] !== val) {
      nums[index] = nums[i]
      index++
    } 
  }
  return index
}

var removeElement = (nums, val) => {
  let index = 0, last = nums.length - 1
  while (index <= last) {
    if (nums[index] === val) {
      nums[index] = nums[last]
      last--
    } else {
      index++
    }
  }
  return index
}

var removeElement = (nums, val) => {
  for (let i = 0; i < nums.length; i++) {
    if (nums[i]===val) {
      nums.splice(i, 1)
      i--
    }
  }
  return nums.length
}

var removeElement = (nums, val) => {
  while (nums.indexOf(val) !== -1) {
    nums.splice(nums.indexOf(val),1)
  }
  return nums.length
}