java實現哈夫曼編碼
阿新 • • 發佈:2019-02-20
哈夫曼演算法
眾所周知,哈夫曼演算法適用於檔案壓縮領域。由於上機需要,就寫了一個Java程式碼實現。
哈夫曼演算法的內容
1.將帶有符號的字母儲存為葉子節點,其權值為符號出現的次數
2.從這些葉子結點中找到權值最小的兩個節點,然後將其合併成一個新節點,即新節點的權值為兩個節點的權值之和,然後刪除這兩個節點。
3.將新節點加入佇列中。重複2-3步驟直到佇列只有一個節點。
哈夫曼的實現
1.定義TreeNode節點
private static class TreeNode implements Comparable<TreeNode>{
TreeNode left;
TreeNode right;
int weight;
char ch;
String code;
public TreeNode(int weight,TreeNode left,TreeNode right) {
this.weight = weight;
this.left = left;
this.right = right;
this.code = "";
}
@Override
public int compareTo(TreeNode o) {
if (this.weight > o.weight) {
return 1;
}else if (this.weight < o.weight) {
return -1;
}else {
return 0;
}
}
}
ch儲存相應字元。code儲存0或1,方便列印字元編碼。
2.實現核心演算法
這裡用了一個TreeSet的容器裝節點,因為它自帶排序功能。(前提是物件為Comparable的子類)
public static TreeNode huffman(TreeMap<Integer, Character> data) {
TreeSet<TreeNode> tNodes = new TreeSet<>();
Set<Integer> weights = data.keySet();
Iterator<Integer> iterator = weights.iterator();
while (iterator.hasNext()) {
int weight = iterator.next();
TreeNode tmp = new TreeNode(weight, null, null);
tmp.ch = data.get(weight);
tNodes.add(tmp);
}
while (tNodes.size() > 1) {
TreeNode leftNode = tNodes.pollFirst();
leftNode.code = "0";
TreeNode rightNode = tNodes.pollFirst();
rightNode.code = "1";
TreeNode newNode = new TreeNode(leftNode.weight+rightNode.weight,
leftNode, rightNode);
tNodes.add(newNode);
}
return tNodes.first();
}
3.得到字元編碼
private static void code(TreeNode t) {
if (t.left != null) {
t.left.code = t.code + t.left.code;
code(t.left);
}
if (t.right != null) {
t.right.code = t.code + t.right.code;
code(t.right);
}
}
4.列印字元編碼結果
public static void print(TreeNode root) {
if (root != null) {
if (root.left == null && root.right == null) {
System.out.println(root.ch + " 編碼:" + root.code);
}else {
print(root.left);
print(root.right);
}
}
}
結果截圖
最後放上完整程式碼:
import java.util.Iterator;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;
public class Huffman {
private static class TreeNode implements Comparable<TreeNode>{
TreeNode left;
TreeNode right;
int weight;
char ch;
String code;
public TreeNode(int weight,TreeNode left,TreeNode right) {
this.weight = weight;
this.left = left;
this.right = right;
this.code = "";
}
@Override
public int compareTo(TreeNode o) {
if (this.weight > o.weight) {
return 1;
}else if (this.weight < o.weight) {
return -1;
}else {
return 0;
}
}
}
public static TreeNode huffman(TreeMap<Integer, Character> data) {
TreeSet<TreeNode> tNodes = new TreeSet<>();
Set<Integer> weights = data.keySet();
Iterator<Integer> iterator = weights.iterator();
while (iterator.hasNext()) {
int weight = iterator.next();
TreeNode tmp = new TreeNode(weight, null, null);
tmp.ch = data.get(weight);
tNodes.add(tmp);
}
while (tNodes.size() > 1) {
TreeNode leftNode = tNodes.pollFirst();
leftNode.code = "0";
TreeNode rightNode = tNodes.pollFirst();
rightNode.code = "1";
TreeNode newNode = new TreeNode(leftNode.weight+rightNode.weight,
leftNode, rightNode);
tNodes.add(newNode);
}
return tNodes.first();
}
private static void code(TreeNode t) {
if (t.left != null) {
t.left.code = t.code + t.left.code;
code(t.left);
}
if (t.right != null) {
t.right.code = t.code + t.right.code;
code(t.right);
}
}
public static void print(TreeNode root) {
if (root != null) {
if (root.left == null && root.right == null) {
System.out.println(root.ch + " 編碼:" + root.code);
}else {
print(root.left);
print(root.right);
}
}
}
public static void main(String[] args) {
TreeMap<Integer, Character> test = new TreeMap<>();
test.put(5, 'f');
test.put(9, 'e');
test.put(12, 'c');
test.put(13, 'b');
test.put(16, 'd');
test.put(45, 'a');
TreeNode root = huffman(test);
code(root);
print(root);
}
}