题目：

题解：

var a, c []int

func countSmaller(nums []int) []int {
    resultList := []int{}
    discretization(nums)
    c = make([]int, len(nums) + 5)
    for i := len(nums) - 1; i >= 0; i-- {
        id := getId(nums[i])
        resultList = append(resultList, query(id - 1))
        update(id)
    }
    for i := 0; i < len(resultList)/2; i++ {
        resultList[i], resultList[len(resultList)-1-i] = resultList[len(resultList)-1-i], resultList[i]
    }
    return resultList
}

func lowBit(x int) int {
    return x & (-x)
}

func update(pos int) {
    for pos < len(c) {
        c[pos]++
        pos += lowBit(pos)
    }
}

func query(pos int) int {
    ret := 0
    for pos > 0 {
        ret += c[pos]
        pos -= lowBit(pos)
    }
    return ret
}

func discretization(nums []int) {
    set := map[int]struct{}{}
    for _, num := range nums {
        set[num] = struct{}{} 
    }
    a = make([]int, 0, len(nums))
    for num := range set {
        a = append(a, num)
    }
    sort.Ints(a)
}

func getId(x int) int {
    return sort.SearchInts(a, x) + 1
}