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AvlTreeMedian.java
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AvlTreeMedian.java
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/*
* Copyright (C) 2014 Pedro Vicente Gómez Sánchez.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.github.pedrovgs.problem36;
import com.github.pedrovgs.binarytree.BinaryNode;
import com.github.pedrovgs.problem15.BinaryTreeInOrder;
import java.util.List;
/**
* Given an AVL (self balanced binary search tree), find the median. Remember you can't just take
* the root element even if the tree is balanced because even with the tree balanced you don't know
* if the median is exactly the root element on a left or right son.
*/
public class AvlTreeMedian {
BinaryTreeInOrder binaryTreeInOrder;
public AvlTreeMedian() {
this.binaryTreeInOrder = new BinaryTreeInOrder();
}
/**
* Iterative algorithm used to find the median of an AVL. This algorithm is based on a property
* of every AVL tree, you can get a sorted collection containing the elements of this tree using
* an in order traversal. Using this property we can get a sorted collection of nodes and then
* find the median. The complexity order of this algorithm is O(N) in time and space terms where
* N
* is the number of nodes in the tree.
*/
public double find(BinaryNode<Integer> root) {
if (root == null) {
throw new IllegalArgumentException("You can't pass a null binary tree to this method.");
}
List<BinaryNode<Integer>> sortedElements = binaryTreeInOrder.getIterative(root);
double median = 0;
if (sortedElements.size() % 2 == 0) {
median = (sortedElements.get(sortedElements.size() / 2).getData() + sortedElements.get(
sortedElements.size() / 2 - 1).getData()) / 2;
} else {
median = sortedElements.get(sortedElements.size() / 2).getData();
}
return median;
}
}