LeetCode - Best Time to Buy and Sell Stock II

문제 설명

You are given an array prices where prices[i] is the price of a given stock on the ith day.

Find the maximum profit you can achieve. You may complete as many transactions as you like (i.e., buy one and sell one share of the stock multiple times).

Note: You may not engage in multiple transactions simultaneously (i.e., you must sell the stock before you buy again).

입출력 예시

Example 1:

Input: prices = [7,1,5,3,6,4]
Output: 7
Explanation: Buy on day 2 (price = 1) and sell on day 3 (price = 5), profit = 5-1 = 4.
Then buy on day 4 (price = 3) and sell on day 5 (price = 6), profit = 6-3 = 3.

Example 2:

Input: prices = [1,2,3,4,5]
Output: 4
Explanation: Buy on day 1 (price = 1) and sell on day 5 (price = 5), profit = 5-1 = 4.
Note that you cannot buy on day 1, buy on day 2 and sell them later, as you are engaging multiple transactions at the same time. You must sell before buying again.

제약사항

Constraints:

1 <= prices.length <= 3 * 104
0 <= prices[i] <= 104

Solution

class Solution {
    public int maxProfit(int[] prices) {

        // 21201
        int profitSum = 0;

        int buyPrirce = -1;
        for (int i = 0; i < prices.length; i++) {

            if (buyPrirce == -1) { // 아직 구매 안함
                // 마지막 인덱스가 아니고, 다음 가격이 현재 가격보다 높아질 경우 구매
                if (i < prices.length - 1 && prices[i] < prices[i + 1]) {
                    buyPrirce = prices[i];
                }
            } else { // 구매 후. 팔지 체크
                // 마지막 인덱스 이거나, 다음 가격이 현재 가격보다 낮아질 경우 팔기
                if (i == prices.length - 1 || prices[i] > prices[i + 1]) {
                    profitSum = profitSum + prices[i] - buyPrirce;
                    buyPrirce = -1;
                }
            }
        }
        return profitSum;
    }
}