Added README.md file for Valid Arrangement of Pairs

Author: kunavamshi

2201-valid-arrangement-of-pairs/README.md

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+<h2><a href="https://leetcode.com/problems/valid-arrangement-of-pairs">Valid Arrangement of Pairs</a></h2> <img src='https://img.shields.io/badge/Difficulty-Hard-red' alt='Difficulty: Hard' /><hr><p>You are given a <strong>0-indexed</strong> 2D integer array <code>pairs</code> where <code>pairs[i] = [start<sub>i</sub>, end<sub>i</sub>]</code>. An arrangement of <code>pairs</code> is <strong>valid</strong> if for every index <code>i</code> where <code>1 &lt;= i &lt; pairs.length</code>, we have <code>end<sub>i-1</sub> == start<sub>i</sub></code>.</p>
+
+<p>Return <em><strong>any</strong> valid arrangement of </em><code>pairs</code>.</p>
+
+<p><strong>Note:</strong> The inputs will be generated such that there exists a valid arrangement of <code>pairs</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> pairs = [[5,1],[4,5],[11,9],[9,4]]
+<strong>Output:</strong> [[11,9],[9,4],[4,5],[5,1]]
+<strong>Explanation:
+</strong>This is a valid arrangement since end<sub>i-1</sub> always equals start<sub>i</sub>.
+end<sub>0</sub> = 9 == 9 = start<sub>1</sub> 
+end<sub>1</sub> = 4 == 4 = start<sub>2</sub>
+end<sub>2</sub> = 5 == 5 = start<sub>3</sub>
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> pairs = [[1,3],[3,2],[2,1]]
+<strong>Output:</strong> [[1,3],[3,2],[2,1]]
+<strong>Explanation:</strong>
+This is a valid arrangement since end<sub>i-1</sub> always equals start<sub>i</sub>.
+end<sub>0</sub> = 3 == 3 = start<sub>1</sub>
+end<sub>1</sub> = 2 == 2 = start<sub>2</sub>
+The arrangements [[2,1],[1,3],[3,2]] and [[3,2],[2,1],[1,3]] are also valid.
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> pairs = [[1,2],[1,3],[2,1]]
+<strong>Output:</strong> [[1,2],[2,1],[1,3]]
+<strong>Explanation:</strong>
+This is a valid arrangement since end<sub>i-1</sub> always equals start<sub>i</sub>.
+end<sub>0</sub> = 2 == 2 = start<sub>1</sub>
+end<sub>1</sub> = 1 == 1 = start<sub>2</sub>
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= pairs.length &lt;= 10<sup>5</sup></code></li>
+	<li><code>pairs[i].length == 2</code></li>
+	<li><code>0 &lt;= start<sub>i</sub>, end<sub>i</sub> &lt;= 10<sup>9</sup></code></li>
+	<li><code>start<sub>i</sub> != end<sub>i</sub></code></li>
+	<li>No two pairs are exactly the same.</li>
+	<li>There <strong>exists</strong> a valid arrangement of <code>pairs</code>.</li>
+</ul>