LeetCode — 122. Best Time to Buy and Sell Stock II

Signal Cat
2 min readJan 11, 2020

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 (i.e., buy one and sell one share of the stock multiple times).

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

Example 1:

Input: [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.

Peak-Valley Solution:



Need to consider every peak immediately following a valley to maximize the profit. If we skip one of the peaks, we lose the profit over that transaction. (C < A +B) So we can just accumulate the profit of transactions between peaks and valleys.

public int maxProfit(int[] prices) {
int maxProfit = 0;
for (int i = 1; i < prices.length; i++) {
if (prices[i] > prices[i-1])
maxProfit += prices[i] - prices[i-1];
return maxProfit;