Content

You are given an array prices where prices[i] is the price of a given stock on the i^th 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 <= 10⁵
0 <= prices[i] <= 10⁴

Solution

1. 动态规划 + 单调栈

Java

class Solution {
    public int maxProfit(int[] prices) {
        // 1 <= prices.length <= 10⁵
        // 0 <= prices[i] <= 10⁴
        int n = prices.length;
        // [0,i]范围内买入并卖出股票的最大收益
        int maxProfit = 0;
        // 单调递减栈
        int minPrice = prices[0];
        for (int i = 1; i < n; i++) {
            minPrice = Math.min(minPrice, prices[i]);
            maxProfit = Math.max(maxProfit, prices[i] - minPrice);
        }
        return maxProfit;
    }
}