求类Split Wise群组支出余额计算算法及Python实现

核心思路 #

要计算用户间的余额，需分两步处理每个支出项，再累加所有支出的结果：

1. 单支出项计算：
   • 计算该支出的人均应摊金额
   • 找出多付（实际支付>应摊）和少付（实际支付<应摊）的用户
   • 少付用户按比例将欠款分给多付用户
2. 总余额累加：将所有支出项中用户间的欠款金额累加，得到最终的互相欠款关系

Python代码实现 #

def calculate_balance(group_expenses):
    # 初始化余额字典，每个用户对应一个空字典记录对其他用户的欠款
    users = group_expenses[0].keys() if group_expenses else []
    balance = {user: {other: 0.0 for other in users if other != user} for user in users}

    for expense in group_expenses:
        # 计算当前支出的总额和人均应摊金额
        total_expense = sum(expense.values())
        num_users = len(expense)
        if num_users == 0:
            continue
        per_person = total_expense / num_users

        # 计算每个用户的收支差额：实际支付 - 应摊金额（正=多付，负=少付）
        diffs = {user: paid - per_person for user, paid in expense.items()}

        # 筛选多付和少付的用户，少付金额取正数表示需要补的钱
        overpaid = {user: diff for user, diff in diffs.items() if diff > 1e-9}  # 避免浮点误差
        underpaid = {user: -diff for user, diff in diffs.items() if diff < -1e-9}
        total_over = sum(overpaid.values())

        if total_over < 1e-9:  # 该支出已平摊，无需处理
            continue

        # 分配少付用户的欠款给多付用户
        for under_user, under_amount in underpaid.items():
            for over_user, over_amount in overpaid.items():
                # 计算当前少付用户需要给多付用户的金额
                amount = under_amount * (over_amount / total_over)
                # 更新余额：under_user 欠 over_user 的金额增加
                balance[under_user][over_user] += amount
                # 反向更新：over_user 欠 under_user 的金额减少（即 under_user 欠 over_user 正数，over_user 欠 under_user 负数）
                balance[over_user][under_user] -= amount

    # 处理浮点精度问题，保留两位小数（可选）
    for user in balance:
        for other in balance[user]:
            balance[user][other] = round(balance[user][other], 2)

    return balance


# 测试示例数据
group_expenses = [
    {"John": 0, "Mary": 0, "Maya": 30},
    {"John": 60, "Mary": 0, "Maya": 0}
]

balance = calculate_balance(group_expenses)
print("John's balance:", balance["John"])  # {'Mary': -20.0, 'Maya': -10.0}
print("Mary's balance:", balance["Mary"])  # {'John': 20.0, 'Maya': 10.0}
print("Maya's balance:", balance["Maya"])  # {'John': 10.0, 'Mary': -10.0}

代码说明 #

1. 初始化余额字典：从第一个支出项提取所有用户，为每个用户创建对应其他用户的欠款记录，初始值为0。
2. 遍历每个支出项：
   • 计算该支出的总额和人均应摊金额。
   • 计算每个用户的收支差额，区分多付和少付用户。
   • 按比例将少付用户的欠款分配给多付用户，更新双向余额记录（比如A欠B10元，等价于B欠A-10元）。
3. 浮点精度处理：使用round保留两位小数，避免浮点运算带来的微小误差。

验证结果 #

运行测试代码后，输出与示例预期完全一致：

• John的余额显示Mary欠他20元，Maya欠他10元（负数表示对方欠自己）。
• Mary的余额显示她欠John20元、欠Maya10元。
• Maya的余额显示她欠John10元，Mary欠她10元。

内容的提问来源于stack exchange，提问作者kiryha