121 Best Time to Buy and Sell Stock

Leetcode

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.

在每个点卖股票最大收益为这个点的股价减去之前的最低价，遍历数组，计算每个点之前到最低价和这个点卖股票的收益，并计算最大收益

class Solution {
    public int maxProfit(int[] prices) {
        if(prices==null || prices.length<=1) return 0;
        int min=Integer.MAX_VALUE;
        int max=0;
        for(int i:prices){
            if(i-min>max) max=i-min;
            if(i<min) min=i;
        }
        return max;
    }
}