/**
 * You are given an array prices where prices[i] is the price of a given stock on the ith day.
 *
 * You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.
 *
 * Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.
 *
 *
 *
 * Example 1:
 *
 * Input: prices = [7,1,5,3,6,4]
 * Output: 5
 * Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
 * Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
 * Example 2:
 *
 * Input: prices = [7,6,4,3,1]
 * Output: 0
 * Explanation: In this case, no transactions are done and the max profit = 0.
 *
 *
 * Constraints:
 *
 * 1 <= prices.length <= 10^5
 * 0 <= prices[i] <= 10^4
 * @see <a href="https://leetcode.com/problems/best-time-to-buy-and-sell-stock/">LeetCode</a>
 */
fun maxProfit(prices: IntArray): Int {
    if (prices.size == 1) {
        return 0
    }
    var lowestPriceSeenSoFar = prices[0]
    var potentialSellingPrice = prices[0]
    var maxProfit = 0
    for (day in prices.indices) {
        val priceToday = prices[day]
        if (priceToday > potentialSellingPrice) {
            potentialSellingPrice = priceToday
            maxProfit = maxOf((potentialSellingPrice - lowestPriceSeenSoFar), maxProfit)
        } else if (priceToday < lowestPriceSeenSoFar) {
            lowestPriceSeenSoFar = priceToday
            potentialSellingPrice = priceToday
        }
    }
    return maxProfit
}

/**
 * You are given an array prices where prices[i] is the price of a given stock on the ith day.
 *
 * You want to maximize your profit by choosing a single day to buy one stock and choosing a different day in the future to sell that stock.
 *
 * Return the maximum profit you can achieve from this transaction. If you cannot achieve any profit, return 0.
 *
 *
 *
 * Example 1:
 *
 * Input: prices = [7,1,5,3,6,4]
 * Output: 5
 * Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
 * Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
 * Example 2:
 *
 * Input: prices = [7,6,4,3,1]
 * Output: 0
 * Explanation: In this case, no transactions are done and the max profit = 0.
 *
 *
 * Constraints:
 *
 * 1 <= prices.length <= 10^5
 * 0 <= prices[i] <= 10^4
 * @see <a href="https://leetcode.com/problems/best-time-to-buy-and-sell-stock/">LeetCode</a>
 */
fun maxProfit(prices: IntArray): Int {
    if (prices.size == 1) {
        return 0
    }
    var lowestPriceSeenSoFar = prices[0]
    var potentialSellingPrice = prices[0]
    var maxProfit = 0
    for (day in prices.indices) {
        val priceToday = prices[day]
        if (priceToday > potentialSellingPrice) {
            potentialSellingPrice = priceToday
            maxProfit = maxOf((potentialSellingPrice - lowestPriceSeenSoFar), maxProfit)
        } else if (priceToday < lowestPriceSeenSoFar) {
            lowestPriceSeenSoFar = priceToday
            potentialSellingPrice = priceToday
        }
    }
    return maxProfit
}
