Immediate Food Delivery II solution and explanation

<pre><code>SELECT ROUND(100.0 * SUM(CASE WHEN order_date = customer_pref_delivery_date THEN 1 ELSE 0 END) / COUNT(*), 2) AS immediate_percentage FROM ( SELECT customer_id, MIN(order_date) AS first_order_date FROM Delivery GROUP BY customer_id ) AS FirstOrders JOIN Delivery ON FirstOrders.customer_id = Delivery.customer_id AND FirstOrders.first_order_date = Delivery.order_date;</code></pre>

<pre><code>import pandas as pd
from io import StringIO

# Simulate database table as DataFrame
data = StringIO(""" delivery_id,customer_id,order_date,customer_pref_delivery_date
1,1,2019-08-01,2019-08-02
2,2,2019-08-02,2019-08-02
3,1,2019-08-11,2019-08-12
4,3,2019-08-24,2019-08-24
5,3,2019-08-21,2019-08-22
6,2,2019-08-11,2019-08-13
7,4,2019-08-09,2019-08-09
""")

df = pd.read_csv(data, parse_dates=['order_date', 'customer_pref_delivery_date'])

# Find first order for each customer
first_orders = df.loc[df.groupby('customer_id')['order_date'].idxmin()]

# Count immediate first orders
total_first_orders = len(first_orders)
immediate_orders = first_orders[first_orders['order_date'] == first_orders['customer_pref_delivery_date']].shape[0]

# Calculate and print the percentage of immediate first orders
immediate_percentage = round((immediate_orders / total_first_orders) * 100, 2)

# Print the result in the required format
print(pd.DataFrame({'immediate_percentage': [immediate_percentage]}))</code></pre>

SELECT ROUND(100.0 * SUM(CASE WHEN order_date = customer_pref_delivery_date THEN 1 ELSE 0 END) / COUNT(*), 2) AS immediate_percentage FROM (SELECT delivery_id, customer_id, order_date, customer_pref_delivery_date, ROW_NUMBER() OVER(PARTITION BY customer_id ORDER BY order_date) as rn FROM Delivery) tmp WHERE rn = 1;

def immediate_percentage(deliveries):
    from collections import defaultdict
    first_orders = defaultdict(lambda: (None, None))
    for delivery_id, customer_id, order_date, pref_date in sorted(deliveries, key=lambda x: (x[1], x[2])):
        if first_orders[customer_id][0] is None:
            first_orders[customer_id] = (order_date, pref_date)
    immediate_count = sum(1 for order_date, pref_date in first_orders.values() if order_date == pref_date)
    total_count = len(first_orders)
    return round(100.0 * immediate_count / total_count, 2)

deliveries = [
    (1, 1, '2019-08-01', '2019-08-02'),
    (2, 2, '2019-08-02', '2019-08-02'),
    (3, 1, '2019-08-11', '2019-08-12'),
    (4, 3, '2019-08-24', '2019-08-24'),
    (5, 3, '2019-08-21', '2019-08-22'),
    (6, 2, '2019-08-11', '2019-08-13'),
    (7, 4, '2019-08-09', '2019-08-09')
]
print(immediate_percentage(deliveries))

#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <iomanip>
using namespace std;

double immediatePercentage(const vector<tuple<int, int, string, string>>& deliveries) {
    map<int, pair<string, string>> firstOrders;
    vector<tuple<int, int, string, string>> sortedDeliveries = deliveries;
    sort(sortedDeliveries.begin(), sortedDeliveries.end(), [](const auto& a, const auto& b) {
        return get<1>(a) < get<1>(b) || (get<1>(a) == get<1>(b) && get<2>(a) < get<2>(b));
    });

    for (const auto& delivery : sortedDeliveries) {
        int customer_id = get<1>(delivery);
        auto [order_date, pref_date] = make_pair(get<2>(delivery), get<3>(delivery));
        if (firstOrders.find(customer_id) == firstOrders.end()) {
            firstOrders[customer_id] = {order_date, pref_date};
        }
    }
    int immediateCount = count_if(firstOrders.begin(), firstOrders.end(), [](const auto& entry) {
        return entry.second.first == entry.second.second;
    });
    return round(100.0 * immediateCount / firstOrders.size() * 100) / 100;
}

int main() {
    vector<tuple<int, int, string, string>> deliveries = {
        {1, 1, "2019-08-01", "2019-08-02"},
        {2, 2, "2019-08-02", "2019-08-02"},
        {3, 1, "2019-08-11", "2019-08-12"},
        {4, 3, "2019-08-24", "2019-08-24"},
        {5, 3, "2019-08-21", "2019-08-22"},
        {6, 2, "2019-08-11", "2019-08-13"},
        {7, 4, "2019-08-09", "2019-08-09"}
    };
    cout << fixed << setprecision(2) << immediatePercentage(deliveries) << endl;
    return 0;
}