我们要解决的核心问题是什么？

描述：模拟矿工不断修改 Nonce，寻找满足特定难度（如哈希以“0000”开头）的值。

import hashlib
import time

def pow_mining(block_data, difficulty):
    print(f"--- [PoW] 开始挖矿：{block_data} ---")
    nonce = 0
    target = "0" * difficulty
    start_time = time.time()
    while True:
        input_string = f"{block_data}{nonce}"
        hash_result = hashlib.sha256(input_string.encode()).hexdigest()
        if hash_result.startswith(target):
            end_time = time.time()
            print(f"✓ 挖矿成功!")
            print(f"哈希值: {hash_result}")
            print(f"随机数(Nonce): {nonce}")
            print(f"耗时: {end_time - start_time:.4f}秒")
            return hash_result
        nonce += 1

# 运行测试
pow_mining("交易数据: A转给B 10个BTC", difficulty=4)

描述：基于“质押权重”的随机抽签算法，质押越多，被选中的概率越高。

import random

class Validator:
    def __init__(self, name, stake):
        self.name = name
        self.stake = stake  # 质押数量

def select_validator_pos(validators):
    total_stake = sum(v.stake for v in validators)
    print(f"\n--- [PoS] 开始抽签 (总质押: {total_stake}) ---")
    pick = random.uniform(0, total_stake)
    current = 0
    for validator in validators:
        current += validator.stake
        if current > pick:
            probability = (validator.stake / total_stake) * 100
            print(f"🎟️ 选中节点: {validator.name}")
            print(f"质押量: {validator.stake}")
            print(f"理论中选率: {probability:.1f}%")
            return validator.name

# 运行测试
nodes = [
    Validator("账户A", 10),
    Validator("大户B", 1000),
    Validator("矿工C", 100),
]
select_validator_pos(nodes)

描述：模拟 PBFT 中的投票阈值检查（N ≥ 3f + 1），其中 N 为节点数，f 为可容忍的作恶节点数。

import random

def pbft_consensus(nodes, message):
    print(f"\n--- [PBFT] 开始共识: {message} ---")
    n = len(nodes)             # 总节点数
    f = (n - 1) // 3           # 可容忍的作恶/故障节点数
    threshold = 2 * f + 1      # 通过所需的赞成票
    votes = 0

    for node in nodes:
        if random.random() < 0.8:  # 模拟80%概率投赞成票
            votes += 1
            print(f"[✔] 节点 {node} -> 投赞成票")
        else:
            print(f"[✘] 节点 {node} -> 拒绝或超时")

    print(f"最终结果: 赞成票 {votes} / 阈值 {threshold}")
    if votes >= threshold:
        print("🎉 达成共识！区块已确认。")
    else:
        print("❌ 共识失败！票数不足。")

# 运行测试
node_list = ["Node_1", "Node_2", "Node_3", "Node_4"]
pbft_consensus(node_list, "提议: 银行A向银行B转账100万")