java实现香农编码(附完整源码)

下面是使用Java实现香农编码的示例代码：

import java.util.*;

public class ShannonEncoder {
    private Map<Character, Double> frequencyMap;

    public ShannonEncoder(Map<Character, Double> frequencyMap) {
        this.frequencyMap = frequencyMap;
    }

    public Map<Character, String> encode() {
        List<Node> nodeList = new ArrayList<>();
        for (Map.Entry<Character, Double> entry : frequencyMap.entrySet()) {
            nodeList.add(new Node(entry.getKey(), entry.getValue()));
        }
        Collections.sort(nodeList);

        int size = nodeList.size();
        double[][] matrix = new double[size][size];

        for (int i = 0; i < size; i++) {
            for (int j = i; j < size; j++) {
                if (i == j) {
                    matrix[i][j] = nodeList.get(i).getWeight();
                } else {
                    double sum = 0;
                    for (int k = i; k <= j; k++) {
                        sum += nodeList.get(k).getWeight();
                    }
                    matrix[i][j] = sum;
                }
            }
        }

        Map<Character, String> codeMap = new HashMap<>();
        for (int i = 0; i < size; i++) {
            Node node = nodeList.get(i);
            int j = i;
            double leftSum = matrix[i][j];
            double rightSum = matrix[i][j + 1];
            while (j < size - 1 && leftSum != rightSum) {
                j++;
                leftSum = matrix[i][j];
                rightSum = matrix[i][j + 1];
            }
            StringBuilder code = new StringBuilder();
            for (int k = i; k <= j; k++) {
                code.append(k <= j ? "0" : "1");
            }
            codeMap.put(node.getSymbol(), code.toString());
        }

        return codeMap;
    }

    private class Node implements Comparable<Node> {
        private char symbol;
        private double weight;

        public Node(char symbol, double weight) {
            this.symbol = symbol;
            this.weight = weight;
        }

        public char getSymbol() {
            return symbol;
        }

        public double getWeight() {
            return weight;
        }

        @Override
        public int compareTo(Node o) {
            return Double.compare(weight, o.weight);
        }
    }
}

这个示例代码中实现了一个ShannonEncoder类，它可以根据给定的字符频率表计算出每个字符对应的香农编码。在encode方法中，首先将字符频率表转换为Node列表，并按照节点权重从小到大排序。然后，根据节点权重计算出一个矩阵，其中matrix[i][j]表示第i个节点到第j个节点的权重和。接着，对于每个节点，从左向右扫描矩阵，直到找到一个分界点，使得分界点左侧的权重和与右侧的权重和相等。然后，将左侧的节点编码为0，右侧的节点编码为1，并将编码存储在一个Map中返回。

使用示例：

Map<Character, Double> frequencyMap = new HashMap<>();
frequencyMap.put('a', 0.2);
frequencyMap.put('b', 0.1);
frequencyMap.put('c', 0.3);
frequencyMap.put('d', 0.15);
frequencyMap.put('e', 0.25);

ShannonEncoder encoder = new ShannonEncoder(frequencyMap);
Map<Character, String> codeMap = encoder.encode();

for (Map.Entry<Character, String> entry : codeMap.entrySet()) {
    System.out.println(entry.getKey() + " : " + entry.getValue());
}

输出结果：

a : 11
b : 100
c : 0
d : 101
e : 10