22w4: add 121 js solution

Author: swiftwind0405

README.md

@@ -321,7 +321,7 @@
 |124|[Binary Tree Maximum Path Sum](https://leetcode.com/problems/binary-tree-maximum-path-sum/)| |Hard|
 |123|[Best Time to Buy and Sell Stock III](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/)| |Hard|
 |122|[Best Time to Buy and Sell Stock II](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/)| [js](./algorithms/bestTimeToBuyAndSellStockIi/Solution.js) |Medium|
-|121|[Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)| [java](./algorithms/bestTimeToBuyAndSellStock/Solution.java) |Medium|
+|121|[Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)| [java](./algorithms/bestTimeToBuyAndSellStock/Solution.java), [js](./algorithms/bestTimeToBuyAndSellStock/Solution.js) |Medium|
 |120|[Triangle](https://leetcode.com/problems/triangle/)| |Medium|
 |119|[Pascal's Triangle II](https://leetcode.com/problems/pascals-triangle-ii/)| |Easy|
 |118|[Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)| |Easy|

algorithms/bestTimeToBuyAndSellStock/Solution.js

@@ -0,0 +1,9 @@
+var maxProfit = function(prices) {
+    let min = prices[0];
+    let max = 0;
+    for (let price of prices) {
+        max = Math.max(max, price - min);
+        min = Math.min(price, min);
+    }
+     return max;
+};