java trie树
字典树查找,Trie,又称字典树、单词查找树,是一种树形结构,用于保存大量的字符串。它的优点是:利用字符串的公共前缀来节约存储空间。
package com.jwetherell.algorithms.data_structures; import java.util.Arrays; /** * A trie, or prefix tree, is an ordered tree data structure that is used to * store an associative array where the keys are usually strings. * * == This is NOT a compact Trie. == * * http://en.wikipedia.org/wiki/Trie * * @author Justin Wetherell <phishman3579@gmail.com> */ public class Trie<C extends CharSequence> { private int size = 0; protected INodeCreator creator = null; protected Node root = null; /** * Default constructor. */ public Trie() { } /** * Constructor with external Node creator. */ public Trie(INodeCreator creator) { this.creator = creator; } /** * Create a new node for sequence. * * @param parent node of the new node. * @param character which represents this node. * @param isWord signifies if the node represents a word. * @return Node which was created. */ protected Node createNewNode(Node parent, Character character, boolean isWord) { return (new Node(parent, character, isWord)); } /** * Add sequence to trie. * * @param seq to add to the trie. * @return True if sequence is added to trie or false if it already exists. */ public boolean add(C seq) { return (this.addSequence(seq)!=null); } /** * Add sequence to trie. * * @param seq to add to the trie. * @return Node which was added to trie or null if it already exists. */ protected Node addSequence(C seq) { if (root==null) { if (this.creator==null) root = createNewNode(null, null, false); else root = this.creator.createNewNode(null, null, false); } int length = (seq.length() - 1); Node prev = root; //For each Character in the input, we'll either go to an already define // child or create a child if one does not exist for (int i = 0; i < length; i++) { Node n = null; Character c = seq.charAt(i); int index = prev.childIndex(c); //If 'prev' has a child which starts with Character c if (index >= 0) { //Go to the child n = prev.getChild(index); } else { //Create a new child for the character if (this.creator==null) n = createNewNode(prev, c, false); else n = this.creator.createNewNode(prev, c, false); prev.addChild(n); } prev = n; } //Deal with the first character of the input string not found in the trie Node n = null; Character c = seq.charAt(length); int index = prev.childIndex(c); //If 'prev' already contains a child with the last Character if (index >= 0) { n = prev.getChild(index); //If the node doesn't represent a string already if (n.isWord == false) { //Set the string to equal the full input string n.character = c; n.isWord = true; size++; return n; } else { //String already exists in Trie return null; } } else { //Create a new node for the input string if (this.creator==null) n = createNewNode(prev, c, true); else n = this.creator.createNewNode(prev, c, true); prev.addChild(n); size++; return n; } } /** * Remove sequence from the trie. * * @param sequence to remove from the trie. * @return True if sequence was remove or false if sequence is not found. */ public boolean remove(C sequence) { if (root == null) return false; //Find the key in the Trie Node previous = null; Node node = root; int length = (sequence.length() - 1); for (int i = 0; i <= length; i++) { char c = sequence.charAt(i); int index = node.childIndex(c); if (index >= 0) { previous = node; node = node.getChild(index); } else { return false; } } if (node.childrenSize > 0) { //The node which contains the input string and has children, just NULL out the string node.isWord = false; } else { //The node which contains the input string does NOT have children int index = previous.childIndex(node.character); //Remove node from previous node previous.removeChild(index); //Go back up the trie removing nodes until you find a node which represents a string while (previous != null && previous.isWord==false && previous.childrenSize == 0) { if (previous.parent != null) { int idx = previous.parent.childIndex(previous.character); if (idx >= 0) previous.parent.removeChild(idx); } previous = previous.parent; } } size--; return true; } /** * Get node which represents the sequence in the trie. * * @param seq to find a node for. * @return Node which represents the sequence or NULL if not found. */ protected Node getNode(C seq) { if (root == null) return null; //Find the string in the trie Node n = root; int length = (seq.length() - 1); for (int i = 0; i <= length; i++) { char c = seq.charAt(i); int index = n.childIndex(c); if (index >= 0) { n = n.getChild(index); } else { //string does not exist in trie return null; } } return n; } /** * Does the trie contain the sequence. * * @param seq to locate in the trie. * @return True if sequence is in the trie. */ public boolean contains(C seq) { Node n = this.getNode(seq); if (n==null || !n.isWord) return false; //If the node found in the trie does not have it's string // field defined then input string was not found return n.isWord; } /** * Number of sequences in the trie. * * @return number of sequences in the trie. */ public int size() { return size; } /** * {@inheritDoc} */ @Override public String toString() { return TriePrinter.getString(this); } protected static class Node { private static final int MINIMUM_SIZE = 2; protected Node[] children = new Node[MINIMUM_SIZE]; protected int childrenSize = 0; protected Node parent = null; protected boolean isWord = false; //Signifies this node represents a word protected Character character = null; //First character that is different the parent's string protected Node(Node parent, Character character, boolean isWord) { this.parent = parent; this.character = character; this.isWord = isWord; } protected void addChild(Node node) { if (childrenSize>=children.length) { children = Arrays.copyOf(children, ((children.length*3)/2)+1); } children[childrenSize++] = node; } protected boolean removeChild(int index) { if (index>=childrenSize) return false; children[index] = null; childrenSize--; System.arraycopy(children, index+1, children, index, childrenSize-index); if (childrenSize>=MINIMUM_SIZE && childrenSize<children.length/2) { children = Arrays.copyOf(children, childrenSize); } return true; } protected int childIndex(Character character) { for (int i = 0; i < childrenSize; i++) { Node c = children[i]; if (c.character.equals(character)) return i; } return Integer.MIN_VALUE; } protected Node getChild(int index) { if (index>=childrenSize) return null; return children[index]; } protected int getChildrenSize() { return childrenSize; } /** * {@inheritDoc} */ @Override public String toString() { StringBuilder builder = new StringBuilder(); if (isWord == true) builder.append("Node=").append(isWord).append("\n"); for (int i=0; i<childrenSize; i++) { Node c = children[i]; builder.append(c.toString()); } return builder.toString(); } } protected static interface INodeCreator { /** * Create a new node for sequence. * * @param parent node of the new node. * @param character which represents this node. * @param isWord signifies if the node represents a word. * @return Node which was created. */ public Node createNewNode(Node parent, Character character, boolean type); } protected static class TriePrinter { public static <C extends CharSequence> void print(Trie<C> trie) { System.out.println(getString(trie)); } public static <C extends CharSequence> String getString(Trie<C> tree) { return getString(tree.root, "", null, true); } protected static <C extends CharSequence> String getString(Node node, String prefix, String previousString, boolean isTail) { StringBuilder builder = new StringBuilder(); String string = null; if (node.character!=null) { String temp = String.valueOf(node.character); if (previousString!=null) string = previousString + temp; else string = temp; } builder.append(prefix + (isTail ? "└── " : "├── ") + ((node.isWord == true) ? ("(" + node.character + ") " + string) : node.character) + "\n"); if (node.children != null) { for (int i = 0; i < node.childrenSize - 1; i++) { builder.append(getString(node.children[i], prefix + (isTail ? " " : "│ "), string, false)); } if (node.childrenSize >= 1) { builder.append(getString(node.children[node.childrenSize - 1], prefix + (isTail ? " " : "│ "), string, true)); } } return builder.toString(); } } }
测试代码
private static boolean testTrie() { { long count = 0; long addTime = 0L; long removeTime = 0L; long beforeAddTime = 0L; long afterAddTime = 0L; long beforeRemoveTime = 0L; long afterRemoveTime = 0L; long memory = 0L; long beforeMemory = 0L; long afterMemory = 0L; //Trie. if (debug>1) System.out.println("Trie."); testNames[testIndex] = "Trie"; count++; if (debugMemory) beforeMemory = DataStructures.getMemoryUse(); if (debugTime) beforeAddTime = System.currentTimeMillis(); Trie<String> trie = new Trie<String>(); for (int i=0; i<unsorted.length; i++) { int item = unsorted[i]; String string = String.valueOf(item); trie.add(string); if (validateStructure && !(trie.size()==i+1)) { System.err.println("YIKES!! "+item+" caused a size mismatch."); handleError(trie); return false; } if (validateContents && !trie.contains(string)) { System.err.println("YIKES!! "+string+" doesn't exist."); handleError(trie); return false; } } if (debugTime) { afterAddTime = System.currentTimeMillis(); addTime += afterAddTime-beforeAddTime; if (debug>0) System.out.println("Trie add time = "+addTime/count+" ms"); } if (debugMemory) { afterMemory = DataStructures.getMemoryUse(); memory += afterMemory-beforeMemory; if (debug>0) System.out.println("Trie memory use = "+(memory/count)+" bytes"); } String invalid = INVALID.toString(); boolean contains = trie.contains(invalid); boolean removed = trie.remove(invalid); if (contains || removed) { System.err.println("Trie invalidity check. contains="+contains+" removed="+removed); return false; } else System.out.println("Trie invalidity check. contains="+contains+" removed="+removed); if (debug>1) System.out.println(trie.toString()); long lookupTime = 0L; long beforeLookupTime = 0L; long afterLookupTime = 0L; if (debugTime) beforeLookupTime = System.currentTimeMillis(); for (int item : unsorted) { String string = String.valueOf(item); trie.contains(string); } if (debugTime) { afterLookupTime = System.currentTimeMillis(); lookupTime += afterLookupTime-beforeLookupTime; if (debug>0) System.out.println("Trie lookup time = "+lookupTime/count+" ms"); } if (debugTime) beforeRemoveTime = System.currentTimeMillis(); for (int i=0; i<unsorted.length; i++) { int item = unsorted[i]; String string = String.valueOf(item); trie.remove(string); if (validateStructure && !(trie.size()==unsorted.length-(i+1))) { System.err.println("YIKES!! "+item+" caused a size mismatch."); handleError(trie); return false; } if (validateContents && trie.contains(string)) { System.err.println("YIKES!! "+string+" still exists."); handleError(trie); return false; } } if (debugTime) { afterRemoveTime = System.currentTimeMillis(); removeTime += afterRemoveTime-beforeRemoveTime; if (debug>0) System.out.println("Trie remove time = "+removeTime/count+" ms"); } contains = trie.contains(invalid); removed = trie.remove(invalid); if (contains || removed) { System.err.println("Trie invalidity check. contains="+contains+" removed="+removed); return false; } else System.out.println("Trie invalidity check. contains="+contains+" removed="+removed); count++; if (debugMemory) beforeMemory = DataStructures.getMemoryUse(); if (debugTime) beforeAddTime = System.currentTimeMillis(); for (int i=unsorted.length-1; i>=0; i--) { int item = unsorted[i]; String string = String.valueOf(item); trie.add(string); if (validateStructure && !(trie.size()==unsorted.length-i)) { System.err.println("YIKES!! "+item+" caused a size mismatch."); handleError(trie); return false; } if (validateContents && !trie.contains(string)) { System.err.println("YIKES!! "+string+" doesn't exists."); handleError(trie); return false; } } if (debugTime) { afterAddTime = System.currentTimeMillis(); addTime += afterAddTime-beforeAddTime; if (debug>0) System.out.println("Trie add time = "+addTime/count+" ms"); } if (debugMemory) { afterMemory = DataStructures.getMemoryUse(); memory += afterMemory-beforeMemory; if (debug>0) System.out.println("Trie memory use = "+(memory/count)+" bytes"); } contains = trie.contains(invalid); removed = trie.remove(invalid); if (contains || removed) { System.err.println("Trie invalidity check. contains="+contains+" removed="+removed); return false; } else System.out.println("Trie invalidity check. contains="+contains+" removed="+removed); if (debug>1) System.out.println(trie.toString()); lookupTime = 0L; beforeLookupTime = 0L; afterLookupTime = 0L; if (debugTime) beforeLookupTime = System.currentTimeMillis(); for (int item : unsorted) { String string = String.valueOf(item); trie.contains(string); } if (debugTime) { afterLookupTime = System.currentTimeMillis(); lookupTime += afterLookupTime-beforeLookupTime; if (debug>0) System.out.println("Trie lookup time = "+lookupTime/count+" ms"); } if (debugTime) beforeRemoveTime = System.currentTimeMillis(); for (int i=0; i<unsorted.length; i++) { int item = unsorted[i]; String string = String.valueOf(item); trie.remove(string); if (validateStructure && !(trie.size()==unsorted.length-(i+1))) { System.err.println("YIKES!! "+item+" caused a size mismatch."); handleError(trie); return false; } if (validateContents && trie.contains(string)) { System.err.println("YIKES!! "+string+" still exists."); handleError(trie); return false; } } if (debugTime) { afterRemoveTime = System.currentTimeMillis(); removeTime += afterRemoveTime-beforeRemoveTime; if (debug>0) System.out.println("Trie remove time = "+removeTime/count+" ms"); } contains = trie.contains(invalid); removed = trie.remove(invalid); if (contains || removed) { System.err.println("Trie invalidity check. contains="+contains+" removed="+removed); return false; } else System.out.println("Trie invalidity check. contains="+contains+" removed="+removed); //sorted long addSortedTime = 0L; long removeSortedTime = 0L; long beforeAddSortedTime = 0L; long afterAddSortedTime = 0L; long beforeRemoveSortedTime = 0L; long afterRemoveSortedTime = 0L; if (debugMemory) beforeMemory = DataStructures.getMemoryUse(); if (debugTime) beforeAddSortedTime = System.currentTimeMillis(); for (int i=0; i<sorted.length; i++) { int item = sorted[i]; String string = String.valueOf(item); trie.add(string); if (validateStructure && !(trie.size()==(i+1))) { System.err.println("YIKES!! "+item+" caused a size mismatch."); handleError(trie); return false; } if (validateContents && !trie.contains(string)) { System.err.println("YIKES!! "+item+" doesn't exist."); handleError(trie); return false; } } if (debugTime) { afterAddSortedTime = System.currentTimeMillis(); addSortedTime += afterAddSortedTime-beforeAddSortedTime; if (debug>0) System.out.println("Trie add time = "+addSortedTime+" ms"); } if (debugMemory) { afterMemory = DataStructures.getMemoryUse(); memory += afterMemory-beforeMemory; if (debug>0) System.out.println("Trie memory use = "+(memory/(count+1))+" bytes"); } contains = trie.contains(invalid); removed = trie.remove(invalid); if (contains || removed) { System.err.println("Trie invalidity check. contains="+contains+" removed="+removed); return false; } else System.out.println("Trie invalidity check. contains="+contains+" removed="+removed); if (debug>1) System.out.println(trie.toString()); lookupTime = 0L; beforeLookupTime = 0L; afterLookupTime = 0L; if (debugTime) beforeLookupTime = System.currentTimeMillis(); for (int item : sorted) { String string = String.valueOf(item); trie.contains(string); } if (debugTime) { afterLookupTime = System.currentTimeMillis(); lookupTime += afterLookupTime-beforeLookupTime; if (debug>0) System.out.println("Trie lookup time = "+lookupTime/(count+1)+" ms"); } if (debugTime) beforeRemoveSortedTime = System.currentTimeMillis(); for (int i=sorted.length-1; i>=0; i--) { int item = sorted[i]; String string = String.valueOf(item); trie.remove(string); if (validateStructure && !(trie.size()==i)) { System.err.println("YIKES!! "+item+" caused a size mismatch."); handleError(trie); return false; } if (validateContents && trie.contains(string)) { System.err.println("YIKES!! "+item+" still exists."); handleError(trie); return false; } } if (debugTime) { afterRemoveSortedTime = System.currentTimeMillis(); removeSortedTime += afterRemoveSortedTime-beforeRemoveSortedTime; if (debug>0) System.out.println("Trie remove time = "+removeSortedTime+" ms"); } contains = trie.contains(invalid); removed = trie.remove(invalid); if (contains || removed) { System.err.println("Trie invalidity check. contains="+contains+" removed="+removed); return false; } else System.out.println("Trie invalidity check. contains="+contains+" removed="+removed); if (testResults[testIndex]==null) testResults[testIndex] = new long[6]; testResults[testIndex][0]+=addTime/count; testResults[testIndex][1]+=removeTime/count; testResults[testIndex][2]+=addSortedTime; testResults[testIndex][3]+=removeSortedTime; testResults[testIndex][4]+=lookupTime/(count+1); testResults[testIndex++][5]+=memory/(count+1); if (debug>1) System.out.println(); } return true; }