solution(javascript): 121. Best Time to Buy and Sell Stock

121. Best Time to Buy and Sell Stock
- JavaScript

Easy/121. Best Time to buy and sell stock/README.md

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+#[121. Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)
+
+## Problem Statement
+
+<p>You are given an array <code>prices</code> where <code>prices[i]</code> is the price of a given stock on the <code>i<sup>th</sup></code> day.</p>
+
+<p>You want to maximize your profit by choosing a <strong>single day</strong> to buy one stock and choosing a <strong>different day in the future</strong> to sell that stock.</p>
+
+<p>Return <em>the maximum profit you can achieve from this transaction</em>. If you cannot achieve any profit, return <code>0</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> prices = [7,1,5,3,6,4]
+<strong>Output:</strong> 5
+<strong>Explanation:</strong> Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 6-1 = 5.
+Note that buying on day 2 and selling on day 1 is not allowed because you must buy before you sell.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> prices = [7,6,4,3,1]
+<strong>Output:</strong> 0
+<strong>Explanation:</strong> In this case, no transactions are done and the max profit = 0.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= prices.length &lt;= 10<sup>5</sup></code></li>
+	<li><code>0 &lt;= prices[i] &lt;= 10<sup>4</sup></code></li>
+</ul>

Easy/121. Best Time to buy and sell stock/Solutioin.js

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+/**
+ * @param {number[]} prices
+ * @return {number}
+ */
+var maxProfit = function (prices) {
+  let l = 0;
+  let r = 1;
+  let max = 0;
+  let profit = 0;
+
+  while (r < prices.length) {
+    profit = prices[r] - prices[l];
+    if (profit > 0) {
+      max = profit > max ? profit : max;
+    } else {
+      l = r;
+    }
+    r++;
+  }
+  return max;
+};

Easy/README.md

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+| **121**  | [Best Time to Buy and Sell Stock](121.%20Best%20Time%20to%20buy%20and%20sell%20stock)                                           |
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