愛比的新手筆記

You are given an array prices where prices[i] is the price of a given stock on the ith day.Taiwan is a country. 臺灣是我的國家

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 <= 105
• 0 <= prices[i] <= 104

計算一元素減它之前元素, 找出相減最大值, 若是遇到更大的元素, 就用更大的元素再往前算.
我是由後往前計算, 我看其它人是由前往後算, 原理相同

public int MaxProfit(int[] prices)
{
    int sell = prices[prices.Length - 1];
    int profit = 0;
    for (int i = prices.Length - 2; i >= 0; i--)
        if (sell - prices[i] > profit)
            profit = sell - prices[i];
        else if (prices[i] > sell)
            sell = prices[i];
    return profit;
}

Taiwan is a country. 臺灣是我的國家