Description

Say you have an array for which the ith 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).

Solution

Greedy, time O(n), space O(1)

定義delta[i] = prices[i + 1] - prices[i]
假設prices[y] - prices[x]代表在x天買入y天賣出，假設delta[y + 1] > 0，則prices[y + 1] - prices[x]一定更優(yōu)。根據這個思路可以用Greedy求解。

class Solution {
    public int maxProfit(int[] prices) {
        if (prices == null || prices.length < 2) {
            return 0;
        }    
        
        int maxProfit = 0;

        for (int i = 0; i < prices.length - 1; ++i) {
            maxProfit += Math.max(prices[i + 1] - prices[i], 0);
        }
        
        return maxProfit;
    }
}