用伪码表示Huffman 树构造算法

Huffman树（也称最优二叉树或霍夫曼树）是一种用于数据压缩的自底向上的贪心算法。以下是使用伪码表示的基本构建过程：

function buildHuffmanTree(freqs):
    if freqs is empty:
        return null (空节点表示叶子节点，频率为0)
    
    sort freqs by frequency in ascending order
    
    create two new nodes with frequencies as their weights
    newNode1 = Node(freq1 of the first pair)
    newNode2 = Node(freq2 of the second pair)
    
    T = PriorityQueue()
    insert newNode1 into T
    insert newNode2 into T
    
    while T has more than one element:
        minNode1 = remove minimum node from T
        minNode2 = remove minimum node from T
        
        combineNodes(minNode1, minNode2) // 创建一个新的节点，其频率等于两个节点的频率之和
        newWeight = minNode1.frequency + minNode2.frequency
        newNode = Node(newWeight)
        
        insert newNode into T
        
    return last node in T (即最小频次的节点，就是根节点)

// combineNodes 函数
function combineNodes(node1, node2):
    newNode = Node(node1.weight + node2.weight)
    newNode.left = node1
    newNode.right = node2
    return newNode

这个伪代码描述了如何通过不断合并频率最低的两个节点创建Huffman树的过程，直到只剩下一个节点为止。