Why my quick-sort get TLE ?

  • 0

    Can anyone help me in finding the problem with the (ugly) code of quicksort ? Get TLE for a middle size input...

    def sortList(self, head):
        :type head: ListNode
        :rtype: ListNode
        if not head: return None
        def quick(lo, hi):
            if not lo or not hi: return None, None
            if lo==hi: return lo, hi
            lhead, ltail = None, None # head and tail for the parts smaller than pivot
            t = lo
            nd = t.next
            while t.next != hi:#partitioning
                nd = t.next
                if nd.val>lo.val: t = t.next
                    if not lhead: lhead = nd
                    if not ltail: ltail = nd
                    elif nd.val==lo.val: #keys equal to lo put it to the end of left part
                        ltail.next, ltail = nd, nd
                        t.next, ltail.next = nd.next, None
                    else: #keys strictly smaller than lo put it to the end of left part
                        t.next = nd.next
                        nd.next = lhead
                        lhead = nd
            # treat the case when t.next=hi
            if hi.val>=lo.val: t, t.next = hi, hi.next
            elif not lhead: lhead,ltail = hi, hi
            else: ltail.next, ltail = hi, hi
            rhead, rtail = (lo.next, t) if t!=lo else (None,None)
            #partition is over, we get 2 segments
            lhead,ltail = quick(lhead,ltail)
            rhead, rtail = quick(rhead, rtail)
            if ltail: ltail.next = lo
            lo.next = rhead
            if rtail: rtail.next = None
            return lhead, rtail
        tail = head
        while tail.next: tail = tail.next
        hd, tl = quick(head, tail)
        return hd

  • 0

    Beacuse the quick sort may be O(N2) in the worst input

  • 0

    But I performed a 3-way qsort (and this is easy as we are using linked lists)

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