Add solution #123

Author: JoshCrozier

README.md

@@ -128,6 +128,7 @@
 120|[Triangle](./0120-triangle.js)|Medium|
 121|[Best Time to Buy and Sell Stock](./0121-best-time-to-buy-and-sell-stock.js)|Easy|
 122|[Best Time to Buy and Sell Stock II](./0122-best-time-to-buy-and-sell-stock-ii.js)|Medium|
+123|[Best Time to Buy and Sell Stock III](./0123-best-time-to-buy-and-sell-stock-iii.js)|Hard|
 124|[Binary Tree Maximum Path Sum](./0124-binary-tree-maximum-path-sum.js)|Hard|
 125|[Valid Palindrome](./0125-valid-palindrome.js)|Easy|
 128|[Longest Consecutive Sequence](./0128-longest-consecutive-sequence.js)|Medium|

solutions/0123-best-time-to-buy-and-sell-stock-iii.js

@@ -0,0 +1,30 @@
+/**
+ * 123. Best Time to Buy and Sell Stock III
+ * https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/
+ * Difficulty: Hard
+ *
+ * You are given an array prices where prices[i] is the price of a given stock on the ith day.
+ *
+ * Find the maximum profit you can achieve. You may complete at most two transactions.
+ *
+ * Note: You may not engage in multiple transactions simultaneously (i.e., you must sell the
+ * stock before you buy again).
+ */
+
+/**
+ * @param {number[]} prices
+ * @return {number}
+ */
+var maxProfit = function(prices) {
+  const costs = [prices[0]];
+  const profits = new Array(prices.length).fill(0);
+
+  for (let i = 0; i < 2; i++) {
+    for (let j = 1; j < prices.length; j++) {
+      costs[j] = Math.min(costs[j - 1], prices[j] - profits[j]);
+      profits[j] = Math.max(profits[j - 1], prices[j] - costs[j]);
+    }
+  }
+
+  return profits[profits.length - 1];
+};