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@@ -1,3 +1,83 @@
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func reversePairs(nums []int) int {
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-
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+ return mergeSort(nums, 0, len(nums)-1)
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+}
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+
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+func mergeSort(nums []int, beg int, end int) int {
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+ if end <= beg {
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+ return 0
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+ }
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+ l, m := beg, beg+(end-beg)/2
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+ r, p, k := m+1, m+1, 0
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+ res := mergeSort(nums, beg, m) + mergeSort(nums, r, end)
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+ merge := make([]int, end-beg+1)
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+ for l <= m {
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+ for ; p <= end && 2*nums[p] < nums[l]; p++ {
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+ } // Advance l once each loop to calculate the cnt of reverse pairs
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+ res += p - m - 1
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+ for r <= end && nums[r] <= nums[l] {
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+ merge[k] = nums[r]
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+ k, r = k+1, r+1
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+ }
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+ merge[k] = nums[l]
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+ k, l = k+1, l+1
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+ }
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+ for r <= end {
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+ merge[k] = nums[r]
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+ k, r = k+1, r+1
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+ }
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+ copy(nums[beg:end+1], merge)
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+ return res
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+}
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+
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+// ---------------------dividing line for TLE binary search algorithm---------------------
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+
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+type ints [][]int
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+
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+func (is ints) search(x int, beg int, end int) int {
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+ for beg <= end {
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+ mid := beg + (end-beg)/2
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+ if is[mid][0] < x {
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+ beg = mid + 1
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+ } else {
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+ end = mid - 1
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+ }
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+ }
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+ return beg
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+}
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+
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+func (is *ints) insert(x int) int {
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+ beg, end := 0, len(*is)
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+ beg = is.search(2*x+1, beg, end-1)
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+ cnt := 0
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+ for i := beg; i < end; i++ {
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+ cnt += (*is)[i][1]
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+ }
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+ if beg == end {
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+ beg--
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+ }
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+ if x < 0 {
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+ beg = is.search(x, 0, end-1)
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+ } else {
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+ beg = is.search(x, 0, beg)
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+ }
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+ if beg == end {
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+ *is = append(*is, []int{x, 1})
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+ } else if (*is)[beg][0] == x {
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+ (*is)[beg][1]++
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+ } else {
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+ nis := make([][]int, end+1)
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+ copy(nis, (*is)[:beg])
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+ nis[beg] = []int{x, 1}
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+ copy(nis[beg+1:], (*is)[beg:])
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+ *is = nis
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+ }
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+ return cnt
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+}
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+
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+func reversePairsTLE(nums []int) (cnt int) {
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+ var is ints = make([][]int, 0)
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+ for _, i := range nums {
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+ cnt += is.insert(i)
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+ }
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+ return
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}
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