[JAVA] 121. Best Time to Buy and Sell Stock

목차

문제

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 <= 105
• 0 <= prices[i] <= 104

아이디어

언제 사서 / 언제 팔지 판단해야한다.

최대한 싸게 사서, 산날 이후 가장 큰 이익을 낼 수 있는 날에 팔아야 한다는걸 생각하자.

풀이

class Solution {
    public int maxProfit(int[] prices) {
    
        int min = Integer.MAX_VALUE;
        int maxProfit = 0;
        int tempProfit = 0;
        
        for (int i = 0; i<prices.length; i++){
            if(prices[i] < min){
                min = prices[i];
            }
            
            tempProfit = prices[i] - min;
            if(maxProfit < tempProfit){
                maxProfit = tempProfit;
            }
            
        }
        
        return maxProfit;
        
    }
}