Customer Placing the Largest Number of Orders — LeetCode 586 Python Solution

The problem

Find the customer who placed the most orders and report their customer number. The test data guarantees exactly one customer holds the record. The Orders table has one row per order: order_number (int, the primary key) and customer_number (int, the customer who placed that order).

Example

Orders table:

| order_number | customer_number |
| ------------ | --------------- |
| 101          | 7               |
| 102          | 4               |
| 103          | 7               |
| 104          | 9               |
| 105          | 7               |

Result:

| customer_number |
| --------------- |
| 7               |

Customer 7 placed three orders while customers 4 and 9 placed one each, so 7 is the answer.

Python solution

import pandas as pd

def customer_with_most_orders(orders: pd.DataFrame) -> pd.DataFrame:
    counts = orders.groupby('customer_number').size()
    max_cnt = counts.max()
    winner = counts[counts == max_cnt].index.min()
    return pd.DataFrame({'customer_number': [int(winner)]})

Complexity

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