【LeetCode】121. The best time to buy and sell stocks

topic

Given an array  prices whose th  i element  prices[i] represents the price of a given stock on the th  i day.

You can only choose  to buy the stock on one day  and   sell it on a different day in the future . Design an algorithm to calculate the maximum profit you can make.

Returns the maximum profit you can make from this trade. If you can't make any profit, return  0 .

Example 1:

Input: [7,1,5,3,6,4]
 Output: 5
 Explanation: buy on day 2 (stock price = 1), sell on day 5 (stock price = 6), Maximum profit = 6-1 = 5. 
     Note that the profit cannot be 7-1 = 6, because the selling price needs to be greater than the buying price; at the same time, you cannot sell the stock before buying.

Example 2:

Input: prices = [7,6,4,3,1]
 Output: 0
 Explanation: In this case, no trades are completed, so the maximum profit is 0.

hint:

• 1 <= prices.length <= 105
• 0 <= prices[i] <= 104

answer

source code

class Solution {
    public int maxProfit(int[] prices) {
        int minPrice = Integer.MAX_VALUE;
        int maxProfit = 0;

        for (int i = 0; i < prices.length; i++) {
            if (prices[i] < minPrice) {
                minPrice = prices[i];
            } else if (prices[i] - minPrice > maxProfit) {
                maxProfit = prices[i] - minPrice;
            }
        }

        return maxProfit;
    }
}

Summarize

Try to refuse brute force cracking, traverse once, constantly update the lowest price and the maximum profit that can be obtained, and return the final maximum profit.