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Commit 6163af3

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Implementation of lowest common ancestor.
1 parent 833341a commit 6163af3

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4 files changed

+184
-3
lines changed

4 files changed

+184
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lines changed

‎.travis.yml‎

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before_script:
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- sudo apt-get install ant-optional
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- export OPTS="-server -Xmx3072M"
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- export JAVA_OPTS="${JAVA_OPTS} ${OPTS}"
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- export ANT_OPTS="${ANT_OPTS} ${OPTS}"
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jdk:
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- oraclejdk8
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- oraclejdk7
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# - oraclejdk7
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# - oraclejdk6
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# - openjdk8
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- openjdk7
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- openjdk6
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# - openjdk6
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env:
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- TEST_SUITE=run_tests
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# - TEST_SUITE=sorts
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script: "ant $TEST_SUITE"
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‎README.md‎

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@@ -63,6 +63,7 @@ This is a collection of algorithms and data structures which I've implement over
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* [Suffix Trie [backed by a Trie]](src/com/jwetherell/algorithms/data_structures/SuffixTrie.java)
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* [Ternary Search Tree](src/com/jwetherell/algorithms/data_structures/TernarySearchTree.java)
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* [Treap](src/com/jwetherell/algorithms/data_structures/Treap.java)
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* [Tree](src/com/jwetherell/algorithms/data_structures/Tree.java)
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* [Tree Map (associative array) [backed by an AVL Tree]](src/com/jwetherell/algorithms/data_structures/TreeMap.java)
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* [Trie](src/com/jwetherell/algorithms/data_structures/Trie.java)
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* [Trie Map (associative array) [backed by a Trie]](src/com/jwetherell/algorithms/data_structures/TrieMap.java)
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* [Edmonds Karp](src/com/jwetherell/algorithms/graph/EdmondsKarp.java)
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* Matching
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- [Turbo Matching](src/com/jwetherell/algorithms/graph/TurboMatching.java)
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* [Lowest common ancestor in tree](src/com/jwetherell/algorithms/data_structures/Tree.java)
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## Search
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* Get index of value in array
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package com.jwetherell.algorithms.data_structures;
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import java.util.ArrayList;
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/**
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* Structure for storing rooted tree which allows to find lowest common ancestor.
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*
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* @param <T> type of value stored in nodes.
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*/
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public class Tree<T> {
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private T value = null;
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private int depth = 0;
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private final ArrayList<Tree<T>> ancestors = new ArrayList<>();
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/**
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* Exception which can be thrown by lowestCommonAncestor function if two
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* nodes are in different trees.
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*
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*/
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public static class NodesNotInSameTreeException extends Exception {}
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/**
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* Finds lower common ancestor of two nodes.
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*
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* Complexity O(log n) where n is the height of the tree.
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*
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* @param node1 first node
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* @param node2 second node
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* @return lower common ancestor
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* @throws NodesNotInSameTreeException if nodes don't have common root
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*/
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public static <S> Tree<S> lowestCommonAncestor(Tree<S> node1, Tree<S> node2) throws NodesNotInSameTreeException {
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if(node1 == node2) return node1;
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else if(node1.depth < node2.depth) return lowestCommonAncestor(node2, node1);
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else if(node1.depth > node2.depth) {
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int diff = node1.depth - node2.depth;
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int jump = 0;
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while(diff > 0) {
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if(diff % 2 == 1)
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node1 = node1.ancestors.get(jump);
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jump++;
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diff /= 2;
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}
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return lowestCommonAncestor(node1, node2);
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}
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else {
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try {
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int step = 0;
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while(1<<(step+1) <= node1.depth) step++;
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while(step >= 0) {
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if(step < node1.ancestors.size() && node1.ancestors.get(step) != node2.ancestors.get(step)) {
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node1 = node1.ancestors.get(step);
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node2 = node2.ancestors.get(step);
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}
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step--;
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}
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return node1.ancestors.get(0);
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} catch (Exception e) {
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throw new NodesNotInSameTreeException();
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}
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}
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}
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/**
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* Creates tree with root only.
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*
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*/
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public Tree() {
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}
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/**
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* Cretes tree with root (storing value) only.
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*
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* @param value value to be stored in root
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*/
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public Tree(T value) {
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this.value = value;
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}
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private Tree(Tree<T> parent) {
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this.ancestors.add(parent);
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this.depth = parent.depth + 1;
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int dist = 0;
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while(true) {
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try {
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this.ancestors.add(this.ancestors.get(dist).ancestors.get(dist));
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dist++;
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} catch (Exception e){
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break;
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}
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}
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}
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public Tree<T> setValue(T value) {
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this.value = value;
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return this;
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}
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/**
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* Creates new child for this node and returns it.
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*
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* Complexity O(log depth)
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*
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* @return added child
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*/
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public Tree<T> addChild() {
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return new Tree<>(this);
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}
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/**
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* Creates new child (storing value) for this node and returns it.
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*
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* Complexity O(log depth)
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*
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* @param value value to be stored in new child
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* @return added child
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*/
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public Tree<T> addChild(T value) {
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return addChild().setValue(value);
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}
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/**
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* Returns value stored in node.
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*
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* @return node's value.
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*/
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public T getValue() {
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return value;
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}
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}
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package com.jwetherell.algorithms.data_structures;
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import org.junit.Test;
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import static org.junit.Assert.*;
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public class TreeTest {
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@Test
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public void largeTreeTest() throws Tree.NodesNotInSameTreeException {
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Tree<Object> root = new Tree<>();
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Tree<Object> left = root.addChild();
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Tree<Object> middle = root.addChild();
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Tree<Object> right = root.addChild();
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//long path
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Tree<Object> v = left;
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for(int i = 0; i<1000; i++)
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v = v.addChild();
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Tree<Object> leftRight = left.addChild();
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assertEquals(Tree.lowestCommonAncestor(v, leftRight), left);
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for(int i = 0; i<2000; i++) {
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leftRight = leftRight.addChild();
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assertEquals(Tree.lowestCommonAncestor(v, leftRight), left);
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}
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assertEquals(Tree.lowestCommonAncestor(middle, right), root);
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assertEquals(Tree.lowestCommonAncestor(root, right), root);
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assertEquals(Tree.lowestCommonAncestor(root, root), root);
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Tree<Object> root2 = new Tree<>();
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boolean thrownException = false;
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try {
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Tree.lowestCommonAncestor(v, root2);
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} catch (Tree.NodesNotInSameTreeException e) {
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thrownException = true;
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}
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assertTrue(thrownException);
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}
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}

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