func removeDuplicates(nums []int) int {
    if len(nums) == 0 {
        return 0
    }
    var prev int
    prevIndex := 0
    for i, num := range nums {
        if i == 0 {
            prev = num
            prevIndex = i
            continue
        }
        if prev != num {
            prevIndex++
            nums[prevIndex] = num
            prev = num
        }
    }
    return prevIndex + 1
}