#!/usr/bin/env python3
# -*- coding: utf-8 -*-

"""
# Meta-info

Author: Nelson Brochado

Created: 18/02/2016

Updated: 29/09/2017

# Description

Min-max heap is a heap that supports find-min and find-max operations in
constant time. Moreover, both remove-min and remove-max are supported in
logarithmic time. It's therefore an useful data structure to represent
double-ended priority queues.

The min-max heap ordering is the following:

    values stored at nodes on even (or min) levels are smaller than or equal to
    values stored at their descendants, whereas values stored at nodes on odd
    (or max) levels are greater than or equal to values stored at their
    descendants.

Even levels are 0, 2, 4, 6, etc., whereas odd levels are 1, 3, 5, 7, etc.

# TODO

- find-kth, i.e. find the kth smallest element in the structure, in O(1) time.
- delete-kth, i.e. delete the kth smallest element, in O(log n) time.

# References

- http://www.akira.ruc.dk/~keld/teaching/algoritmedesign_f03/Artikler/02/Atkinson86.pdf
- http://www.diku.dk/forskning/performance-engineering/Jesper/heaplab/heapsurvey_html/node11.html
- http://www.math.clemson.edu/~warner/M865/HeapDelete.html](http://www.math.clemson.edu/~warner/M865/HeapDelete.html
"""

import math

from ands.ds.BinaryHeap import BinaryHeap

__all__ = ["MinMaxHeap", "is_min_max_heap"]


class MinMaxHeap(BinaryHeap):
    """Sub-class of BinaryHeap, and thus provides the same public interface,
    but in addition provides four more operations:

    - find_max
    - find_min
    - remove_max
    - remove_min"""

    def __init__(self, ls=None):
        BinaryHeap.__init__(self, ls)

    def find_max(self) -> object:
        """Returns the greatest element in this MinMaxHeap.

        Time complexity: O(1)."""
        if not self.is_empty():
            return self.heap[self._find_max_index()]

    def find_min(self) -> object:
        """Returns the smallest element in this MinMaxHeap.

        Time complexity: O(1)."""
        if not self.is_empty():
            return self.heap[0]

    def remove_max(self) -> object:
        """Removes and returns the greatest element in this MinMaxHeap.

        Time complexity: O(log(n))."""
        assert is_min_max_heap(self)

        if not self.is_empty():
            i = self._find_max_index()

            if i == self.size - 1:
                m = self.heap.pop()
                assert is_min_max_heap(self)
                return m

            self._swap(i, self.size - 1)
            m = self.heap.pop()
            self._push_up(i)
            self._push_down(i)
            assert is_min_max_heap(self)
            return m

    def remove_min(self) -> object:
        """Removes and returns the smallest element in this MinMaxHeap.

        Time complexity: O(log(n))."""
        if not self.is_empty():
            if self.size == 1:
                m = self.heap.pop()
                assert is_min_max_heap(self)
                return m

            self._swap(0, self.size - 1)
            m = self.heap.pop()
            self._push_up(0)
            self._push_down(0)
            assert is_min_max_heap(self)
            return m

    def _push_down(self, i: int) -> None:
        """This operation is also called "bubble-down" or "shift-down"."""
        if self._is_on_even_level(i):
            self._push_down_min(i)
        else:
            self._push_down_max(i)

    def _push_down_min(self, i: int) -> None:
        """Helper method for self._push_down."""
        if self._has_children(i):
            m = self._index_of_min(i)

            if self._is_grandchild(m, i):
                if self.heap[m] < self.heap[i]:
                    self._swap(i, m)

                    mp = self._parent_index(m)
                    if mp != -1 and self.heap[m] > self.heap[mp]:
                        self._swap(m, mp)
                    self._push_down_min(m)

            else:  # self.heap[m] is a child of self.heap[i].
                if self.heap[m] < self.heap[i]:
                    self._swap(i, m)

    def _push_down_max(self, i: int) -> None:
        """Helper method for self._push_down."""
        if self._has_children(i):
            m = self._index_of_max(i)

            if self._is_grandchild(m, i):
                if self.heap[m] > self.heap[i]:
                    self._swap(i, m)

                    mp = self._parent_index(m)
                    if mp != -1 and self.heap[m] < self.heap[mp]:
                        self._swap(m, mp)
                    self._push_down_max(m)

            else:  # self.heap[m] is a child of self.heap[i].
                if self.heap[m] > self.heap[i]:
                    self._swap(i, m)

    def _push_up(self, i: int) -> None:
        """This operation is also called "bubble-up" or "shift-up"."""
        p = self._parent_index(i)

        # Let x be the element at index i.
        # If x has a parent at position p, we call it y.
        if self._is_on_even_level(i):
            if p != -1 and self.heap[i] > self.heap[p]:
                # If x is greater than y, swap x with y.
                # Now, x is at index p, and y at index i.
                # _push_up_max from the new index of x, i.e. p.
                self._swap(i, p)
                self._push_up_max(p)
            else:
                # x does not have a parent OR x <= y.
                self._push_up_min(i)
        else:
            # Odd or max level.
            if p != -1 and self.heap[i] < self.heap[p]:
                self._swap(i, p)
                self._push_up_min(p)
            else:
                self._push_up_max(i)

    def _push_up_min(self, i: int) -> None:
        """Helper method for self._push_up."""
        g = self._grandparent_index(i)
        # Let x be the element at index i.
        # If x has a grandparent at position g, we call it z.

        # If the z exists and x is smaller than z, swap x and z.
        # Now, x is at index g and z at index i.
        if g != -1 and self.heap[i] < self.heap[g]:
            self._swap(i, g)
            self._push_up_min(g)

    def _push_up_max(self, i: int) -> None:
        """Helper method for self._push_up."""
        g = self._grandparent_index(i)
        if g != -1 and self.heap[i] > self.heap[g]:
            self._swap(i, g)
            self._push_up_max(g)

    def _find_max_index(self) -> int:
        """Returns the index of the maximum element in this MinMaxHeap.

        Time complexity: O(1)."""
        if self.is_empty():
            return -1
        elif self.size == 1:
            return 0
        elif self.size == 2:
            return 1
        else:
            return 1 if self.heap[1] > self.heap[2] else 2

    def _index_of_min(self, i: int) -> int:
        """Returns the index of the smallest element among the children and
        grandchildren of the node at index i.

        Time complexity: O(1)."""
        m = l = self._left_index(i)
        r = self._right_index(i)

        if r != -1 and self.heap[r] < self.heap[m]:
            m = r

        if l != -1:
            gll = self._left_index(l)
            if gll != -1 and self.heap[gll] < self.heap[m]:
                m = gll
            glr = self._right_index(l)
            if glr != -1 and self.heap[glr] < self.heap[m]:
                m = glr

        if r != -1:
            grl = self._left_index(r)
            if grl != -1 and self.heap[grl] < self.heap[m]:
                m = grl
            grr = self._right_index(r)
            if grr != -1 and self.heap[grr] < self.heap[m]:
                m = grr

        return m

    def _index_of_max(self, i: int) -> int:
        """Returns the index of the largest element among the children and
        grandchildren of the node at index i.

        Time complexity: O(1)."""
        m = l = self._left_index(i)
        r = self._right_index(i)

        if r != -1 and self.heap[r] > self.heap[m]:
            m = r

        if l != -1:
            gll = self._left_index(l)
            if gll != -1 and self.heap[gll] > self.heap[m]:
                m = gll
            glr = self._right_index(l)
            if glr != -1 and self.heap[glr] > self.heap[m]:
                m = glr

        if r != -1:
            grl = self._left_index(r)
            if grl != -1 and self.heap[grl] > self.heap[m]:
                m = grl
            grr = self._right_index(r)
            if grr != -1 and self.heap[grr] > self.heap[m]:
                m = grr

        return m

    def _has_children(self, i: int) -> bool:
        """Returns true if the node at index i has at least one child, false
        otherwise.

        Time complexity: O(1)."""
        assert self._is_good_index(i)
        return self._left_index(i) != -1 or self._right_index(i) != -1

    def _is_child(self, c: int, i: int) -> bool:
        """Returns true if c is a child of i, false otherwise.

        Time complexity: O(1)."""
        assert self._is_good_index(c) and self._is_good_index(i)
        return c == self._left_index(i) or c == self._right_index(i)

    def _is_grandchild(self, g: int, i: int) -> bool:
        """Returns true if g is a grandchild of i, false otherwise.

        Time complexity: O(1)."""
        l = self._left_index(i)
        if l == -1:
            assert self._right_index(i) == -1
            assert self._is_good_index(g)
            return False
        r = self._right_index(i)
        if r == -1:
            return self._is_child(g, l)
        else:
            return self._is_child(g, l) or self._is_child(g, r)

    def _grandparent_index(self, i: int) -> int:
        """Returns the grandparent's index of the node at index i.

        -1 is returned either if i has not a parent or the parent of i does not
        have a parent.

        Time complexity: O(1)."""
        p = self._parent_index(i)
        return -1 if p == -1 else self._parent_index(p)

    def _is_on_even_level(self, i: int) -> bool:
        """Returns true if node at index i is on a even-level, i.e., if i is on
        a level multiple of 2.

        Time complexity: O(int(log(i + 1) % 2) == 0)."""
        assert self._is_good_index(i)
        return int(math.log2(i + 1) % 2) == 0

    def _is_on_odd_level(self, i: int) -> bool:
        """Returns true when self._is_on_even_level(i) returns false, and
        vice-versa."""
        return not self._is_on_even_level(i)


def is_min_max_heap(h: MinMaxHeap) -> bool:
    """Returns true if h is a valid MinMaxHeap object, false otherwise."""
    if not isinstance(h, MinMaxHeap):
        return False

    if h.heap:

        if h.size == 1:
            return True
        if h.size == 2:
            return max(h.heap) == h.heap[1] and min(h.heap) == h.heap[0]
        if h.size >= 3:
            if (h.heap[0] != min(h.heap) or
                    (h.heap[1] != max(h.heap) and
                     h.heap[2] != max(h.heap))):
                return False

        # i is the index of the current node.
        for i, item in reversed(list(enumerate(h.heap))):
            l = h._left_index(i)
            r = h._right_index(i)

            # If item has a right child but not a left child, then this heap is
            # not well structured.
            if r != -1 and l == -1:
                return False

            if h._is_on_even_level(i):
                # If item is on an even (or min) level, then item should be
                # smaller or equal than its descendants.
                if l != -1 and item > h.heap[l]:
                    return False
                if r != -1 and item > h.heap[r]:
                    return False
            else:  # odd (or max) level
                # If item is on an odd (or max) level, then item should be
                # greater or equal than descendants.
                if l != -1 and item < h.heap[l]:
                    return False
                if r != -1 and item < h.heap[r]:
                    return False
    return True
