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leetcode/problem/maximum-alternating-subsequence-sum.html

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+<p>The <strong>alternating sum</strong> of a <strong>0-indexed</strong> array is defined as the <strong>sum</strong> of the elements at <strong>even</strong> indices <strong>minus</strong> the <strong>sum</strong> of the elements at <strong>odd</strong> indices.</p>
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+
+
+<ul>
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+	<li>For example, the alternating sum of <code>[4,2,5,3]</code> is <code>(4 + 5) - (2 + 3) = 4</code>.</li>
+
+</ul>
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+
+
+<p>Given an array <code>nums</code>, return <em>the <strong>maximum alternating sum</strong> of any subsequence of </em><code>nums</code><em> (after <strong>reindexing</strong> the elements of the subsequence)</em>.</p>
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+
+
+<ul>
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+</ul>
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+
+
+<p>A <strong>subsequence</strong> of an array is a new array generated from the original array by deleting some elements (possibly none) without changing the remaining elements&#39; relative order. For example, <code>[2,7,4]</code> is a subsequence of <code>[4,<u>2</u>,3,<u>7</u>,2,1,<u>4</u>]</code> (the underlined elements), while <code>[2,4,2]</code> is not.</p>
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+
+
+<p>&nbsp;</p>
+
+<p><strong>Example 1:</strong></p>
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+
+
+<pre>
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+<strong>Input:</strong> nums = [<u>4</u>,<u>2</u>,<u>5</u>,3]
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+<strong>Output:</strong> 7
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+<strong>Explanation:</strong> It is optimal to choose the subsequence [4,2,5] with alternating sum (4 + 5) - 2 = 7.
+
+</pre>
+
+
+
+<p><strong>Example 2:</strong></p>