下面代码实现了哈夫曼编码，则横线处应填写的代码是（ ）。class Symbol: def __init__(self, ch='', freq=0, code=''): self.ch = ch self.freq = freq self.code = code class Node: def __init__(self, w=0, l=-1, r=-1, sym=-1): self.w = w self.l = l self.r = r self.sym = sym def pop_min_node(nodes, leaf_idx, n, pA, internal_idx, pB): if pA[0] = len(internal_idx) or nodes[leaf_idx[pA[0]]].w <= nodes[internal_idx[pB[0]]].w): res = leaf_idx[pA[0]] pA[0] += 1 return res else: res = internal_idx[pB[0]] pB[0] += 1 return res def dfs_build_codes(u, nodes, sym_list, path): if u == -1: return if nodes[u].sym != -1: sym_list[nodes[u].sym].code = ''.join(path) return path.append('0') dfs_build_codes(nodes[u].l, nodes, sym_list, path) path.pop() path.append('1') dfs_build_codes(nodes[u].r, nodes, sym_list, path) path.pop() def build_huffman_codes(sym_list): n = len(sym_list) for sym in sym_list: sym.code = '' if n <= 0: return -1 if n == 1: sym_list[0].code = '0' return 0 nodes = [] leaf_idx = [] for i in range(n): leaf_idx.append(len(nodes)) nodes.append(Node(sym_list[i].freq, -1, -1, i)) leaf_idx.sort(key=lambda x: (nodes[x].w, nodes[x].sym)) internal_idx = [] pA = [0] pB = [0] for k in range(1, n): x = pop_min_node(nodes, leaf_idx, n, pA, internal_idx, pB) y = pop_min_node(nodes, leaf_idx, n, pA, internal_idx, pB) z = len(nodes) # 补全缺失的构建内部节点代码（原代码空白处） nodes.append(Node(w=nodes[x].w + nodes[y].w, l=x, r=y, sym=-1)) internal_idx.append(z) root = internal_idx[-1] if internal_idx else -1 path = [] dfs_build_codes(root, nodes, sym_list, path) return root if __name__ == "__main__": syms = [ Symbol('A', 5), Symbol('B', 9), Symbol('C', 12), Symbol('D', 13), Symbol('E', 16), Symbol('F', 45) ] root = build_huffman_codes(syms) print(f"哈夫曼树根节点下标：{root}") for sym in syms: print(f"字符 '{sym.ch}' (频率 {sym.freq})：编码 {sym.code}")

正确答案：A

试卷来源：202512 CCF-GESP编程能力等级认证Python六级真题

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