哈夫曼树与哈夫曼编码

哈夫曼编码使用在编码领域，可以有效的压缩存储空间，我们的程序分为两部分，第一部分是哈夫曼树的节点类，定义了它的码值，权重（即出现频率），左右孩子节点与双亲节点，初始化时后三者都是空的。

代码如下

public class HTNode {
private char data;
private int weight;
private HTNode parent;
private HTNode left;
private HTNode right;

public HTNode(char data, int weight) {
this.data = data;
this.weight = weight;
this.parent=null;
this.left=null;
this.right=null;
}
public char getData() {
return data;
}
public void setData(char data) {
this.data = data;
}
public int getWeight() {
return weight;
}
public void setWeight(int weight) {
this.weight = weight;
}
public HTNode getParent() {
return parent;
}
public void setParent(HTNode parent) {
this.parent = parent;
}
public HTNode getLeft() {
return left;
}
public void setLeft(HTNode left) {
this.left = left;
}
public HTNode getRight() {
return right;
}
public void setRight(HTNode right) {
this.right = right;
}

}

之后我们编写一个工厂类，用于生成哈夫曼树与哈夫曼编码，只需输入一个由树节点组成的数组，即可以得到对应的哈夫曼编码，代码如下

public class TreeBuilder {

public static HTNode[] createHT(HTNode[] nodes){
int len=nodes.length*2-1;
HTNode[] tree=new HTNode[len];
for(int i=0;i<nodes.length;i++){
tree[i]=new HTNode(nodes[i].getData(),nodes[i].getWeight());
}
for(int i=nodes.length;i<len;i++){
tree[i]=new HTNode(' ', 0);
}
for(int i=nodes.length;i<len;i++){
int min1=9999;
int min2=9999;
int left=-1;
int right=-1;
for(int k=0;k<i;k++){
if(tree[k].getParent()==null){
if(tree[k].getWeight()<=min1){
min2=min1;
right=left;
min1=tree[k].getWeight();
left=k;
}
else{
if(tree[k].getWeight()<min2){
min2=tree[k].getWeight();
right=k;
}
}
}
}
tree[i].setWeight(tree[right].getWeight()+tree[left].getWeight());
tree[i].setLeft(tree[left]);
tree[i].setRight(tree[right]);
tree[left].setParent(tree[i]);
tree[right].setParent(tree[i]);
}
return tree;
//		for(int i=0;i<len;i++){
//			System.out.print(tree[i].getWeight()+" ");
//		}
}

public static void createHTCode(HTNode[] nodes){
int len=nodes.length*2-1;
HTNode[] tree=new HTNode[len];
tree=createHT(nodes);
HTNode p=null;
HTNode parent=null;
StringBuilder[] codes=new StringBuilder[nodes.length];

for(int i=0;i<nodes.length;i++){
p=tree[i];
parent=p.getParent();
while(parent!=null){
if(parent.getLeft()==p){
if(codes[i]==null){
codes[i]=new StringBuilder("0");
}
else{
//						sb.Insert(0, "tt");
codes[i].insert(0, "0");
}
}
if(parent.getRight()==p){
if(codes[i]==null){
codes[i]=new StringBuilder("1");
}
else{
codes[i].insert(0, "1");
}
}
p=parent;
parent=p.getParent();
}
}
for(int i=0;i<codes.length;i++){
System.out.println(codes[i]);
}

}

public static void main(String args[]){
HTNode n1=new HTNode('a',3);
HTNode n2=new HTNode('b',4);
HTNode n3=new HTNode('a',5);
HTNode n4=new HTNode('a',6);
HTNode[] nodes={n1,n2,n3,n4};
createHTCode(nodes);
}

}