Leetcode–Best Time to Buy and Sell Stock II

The Problem:

Say you have an array for which the i^th element is the price of a given stock on day i.

Design an algorithm to find the maximum profit. You may complete as many transactions as you like (ie, buy one and sell one share of the stock multiple times). However, you may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).

Notes:

1. Observe a simple rule that each time detects a drop in price, should sell it before drop, and then buy at the drop. So use greedy. Remember to sell in the last day even no drop.

Java Solution

public class Solution {
    public int maxProfit(int[] prices) {
        if(prices.length<=1) 
            return 0;
        int profit = 0;
        int buy = prices[0];
        for(int i = 1; i < prices.length; i++){
            // sell only prices go down
            if(prices[i] < prices[i-1]){
                profit += prices[i-1]-buy;
                buy = prices[i];
            }
            // sell in last day even not go down
            else if(i==prices.length-1){
                profit += prices[i]-buy;
            }
        }
        return profit;
    }
}

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