貪心算法-哈夫曼樹

貪心的思想很簡單，關鍵在於用一個什麼樣的結構來實現貪心過程。

package Section9;

import java.util.Queue;
import java.util.Iterator;
import java.util.LinkedList;


/*第九章  貪婪算法   Huffman編碼*/

public class Huffman {

/**
     * @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
        double[] P = {0.35,0.1,0.2,0.2,0.15};
char[] CC = {'B','-','C','D','A'};

        TreeNode root = Huffman(P,CC);

        System.out.println(root.p);    
    }


public static TreeNode Huffman(double[] P,char[] CC){
//輸入要編碼的字符的概率數組，返回huffman樹的root結點
        int n = P.length;
        TreeNode[] Roots = new TreeNode[n];    //當前root結點數組
        Queue<TreeNode> queue = new LinkedList<TreeNode>();        //注意java中Queue是一個接口

//樹隊列的初始化
        for(int i = 0;i < n;i++)
        {
            Roots[i] = new TreeNode(P[i]);
            Roots[i].c = CC[i];
            queue.add(Roots[i]);
        }

while(queue.size() != 1)
        {
//找到最小的結點並刪除
            TreeNode leftNode = queue.peek();
            Iterator it = queue.iterator();
while(it.hasNext())
            {
                TreeNode node = (TreeNode) it.next();
if(node.p < leftNode.p)
                    leftNode = node;
            }
            queue.remove(leftNode);

//找到最小的結點並刪除
            TreeNode rightNode = queue.peek();
            it = queue.iterator();
while(it.hasNext())
            {
                TreeNode node = (TreeNode) it.next();
if(node.p < rightNode.p)
                    rightNode = node;
            }
            queue.remove(rightNode);

//用上述最小的2個結點構造一顆樹，加入樹隊列
            TreeNode Root = new TreeNode(leftNode.p + rightNode.p);
            Root.leftNode = leftNode;
            Root.rightNode = rightNode;

            queue.add(Root);
        }

return queue.peek();
    }
}

描述略。