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Author: NinePiece2

Solutions/0376-wiggle-subsequence/README.md

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+<p>A <strong>wiggle sequence</strong> is a sequence where the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with one element and a sequence with two non-equal elements are trivially wiggle sequences.</p>
+
+<ul>
+	<li>For example, <code>[1, 7, 4, 9, 2, 5]</code> is a <strong>wiggle sequence</strong> because the differences <code>(6, -3, 5, -7, 3)</code> alternate between positive and negative.</li>
+	<li>In contrast, <code>[1, 4, 7, 2, 5]</code> and <code>[1, 7, 4, 5, 5]</code> are not wiggle sequences. The first is not because its first two differences are positive, and the second is not because its last difference is zero.</li>
+</ul>
+
+<p>A <strong>subsequence</strong> is obtained by deleting some elements (possibly zero) from the original sequence, leaving the remaining elements in their original order.</p>
+
+<p>Given an integer array <code>nums</code>, return <em>the length of the longest <strong>wiggle subsequence</strong> of </em><code>nums</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [1,7,4,9,2,5]
+<strong>Output:</strong> 6
+<strong>Explanation:</strong> The entire sequence is a wiggle sequence with differences (6, -3, 5, -7, 3).
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [1,17,5,10,13,15,10,5,16,8]
+<strong>Output:</strong> 7
+<strong>Explanation:</strong> There are several subsequences that achieve this length.
+One is [1, 17, 10, 13, 10, 16, 8] with differences (16, -7, 3, -3, 6, -8).
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> nums = [1,2,3,4,5,6,7,8,9]
+<strong>Output:</strong> 2
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= nums.length &lt;= 1000</code></li>
+	<li><code>0 &lt;= nums[i] &lt;= 1000</code></li>
+</ul>
+
+<p>&nbsp;</p>
+<p><strong>Follow up:</strong> Could you solve this in <code>O(n)</code> time?</p>

Solutions/0376-wiggle-subsequence/solution.py

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+class Solution:
+    def wiggleMaxLength(self, nums: List[int]) -> int:
+        # n = len(nums)
+        # dp1 = [1] * n
+        # dp2 = [1] * n
+        # result = 1
+
+        # for i in range(1, n):
+        #     for j in range(i):
+        #         if nums[i] < nums[j]:
+        #             dp1[i] = max(dp1[i], dp2[j] + 1)
+        #         elif nums[i] > nums[j]:
+        #             dp2[i] = max(dp2[i], dp1[j] + 1)
+        #     result = max(result, dp1[i], dp2[i])
+
+        # return result
+
+        inc, dec = 1, 1
+        for num1, num2 in pairwise(nums):
+            if num2 > num1:
+                inc = dec + 1
+            elif num2 < num1:
+                dec = inc + 1
+        return max(inc, dec)