Product Price at a Given Date solution and explanation

from collections import defaultdict

def product_prices_on_date(products):
    # Default price before any change
    base_price = 10
    target_date = '2019-08-16'
    product_latest = defaultdict(lambda: base_price)
    
    for product_id, new_price, change_date in sorted(products, key=lambda x: (x[0], x[2])):
        if change_date <= target_date:
            product_latest[product_id] = new_price
    
    return [[product_id, product_latest[product_id]] for product_id in product_latest]

function productPricesOnDate(products) {
    const basePrice = 10;
    const targetDate = '2019-08-16';
    const productLatest = {};

    products.sort((a, b) => {
        if (a[0] === b[0]) {
            return new Date(a[2]) - new Date(b[2]);
        }
        return a[0] - b[0];
    });

    for (const [product_id, new_price, change_date] of products) {
        if (change_date <= targetDate) {
            productLatest[product_id] = new_price;
        }
    }

    return Object.entries(productLatest).map(([product_id, price]) => ({
        product_id: parseInt(product_id, 10),
        price: price || basePrice,
    }));
}

#include <iostream>
#include <vector>
#include <map>
#include <tuple>
#include <string>
#include <algorithm>

using namespace std;

vector<pair<int, int>> productPricesOnDate(vector<tuple<int, int, string>> &products) {
    int basePrice = 10;
    string targetDate = "2019-08-16";
    map<int, int> productLatestPrice;
    
    for (const auto &[product_id, new_price, change_date] : products) {
        if (change_date <= targetDate) {
            productLatestPrice[product_id] = max(productLatestPrice[product_id], new_price);
        }
    }

    vector<pair<int, int>> result;
    for (const auto &[product_id, price]: productLatestPrice) {
        result.emplace_back(product_id, (price != 0) ? price : basePrice);
    }
    
    return result;
}

using System;
using System.Collections.Generic;

public class Solution {
    public List<(int, int)> ProductPricesOnDate(List<(int, int, DateTime)> products) {
        int basePrice = 10;
        DateTime targetDate = new DateTime(2019, 8, 16);
        var productLatestPrice = new Dictionary<int, int>();

        foreach (var (product_id, new_price, change_date) in products) {
            if (change_date <= targetDate) {
                if (!productLatestPrice.ContainsKey(product_id) || productLatestPrice[product_id] < new_price) {
                    productLatestPrice[product_id] = new_price;
                }
            }
        }

        var result = new List<(int, int)>();
        foreach (var kvp in productLatestPrice) {
            result.Add((kvp.Key, kvp.Value != 0 ? kvp.Value : basePrice));
        }

        return result;
    }
}

# Write your MySQL query statement below
WITH
    T AS (SELECT DISTINCT product_id FROM Products),
    P AS (
        SELECT product_id, new_price AS price
        FROM Products
        WHERE
            (product_id, change_date) IN (
                SELECT product_id, MAX(change_date) AS change_date
                FROM Products
                WHERE change_date <= '2019-08-16'
                GROUP BY 1
            )
    )
SELECT product_id, IFNULL(price, 10) AS price
FROM
    T
    LEFT JOIN P USING (product_id);

# Write your MySQL query statement below
WITH
    P AS (
        SELECT p1.product_id, new_price, change_date
        FROM
            (
                SELECT DISTINCT product_id
                FROM Products
            ) AS p1
            LEFT JOIN Products AS p2
                ON p1.product_id = p2.product_id AND p2.change_date <= '2019-08-16'
    ),
    T AS (
        SELECT
            *,
            RANK() OVER (
                PARTITION BY product_id
                ORDER BY change_date DESC
            ) AS rk
        FROM P
    )
SELECT product_id, IFNULL(new_price, 10) AS price
FROM T
WHERE rk = 1;