Sync LeetCode submission Runtime - 846 ms (61.26%), Memory - 18.1 MB (74.83%)

Author: jimit105

0905-length-of-longest-fibonacci-subsequence/README.md

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+<p>A sequence <code>x<sub>1</sub>, x<sub>2</sub>, ..., x<sub>n</sub></code> is <em>Fibonacci-like</em> if:</p>
+
+<ul>
+	<li><code>n &gt;= 3</code></li>
+	<li><code>x<sub>i</sub> + x<sub>i+1</sub> == x<sub>i+2</sub></code> for all <code>i + 2 &lt;= n</code></li>
+</ul>
+
+<p>Given a <b>strictly increasing</b> array <code>arr</code> of positive integers forming a sequence, return <em>the <strong>length</strong> of the longest Fibonacci-like subsequence of</em> <code>arr</code>. If one does not exist, return <code>0</code>.</p>
+
+<p>A <strong>subsequence</strong> is derived from another sequence <code>arr</code> by deleting any number of elements (including none) from <code>arr</code>, without changing the order of the remaining elements. For example, <code>[3, 5, 8]</code> is a subsequence of <code>[3, 4, 5, 6, 7, 8]</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr = [1,2,3,4,5,6,7,8]
+<strong>Output:</strong> 5
+<strong>Explanation:</strong> The longest subsequence that is fibonacci-like: [1,2,3,5,8].</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> arr = [1,3,7,11,12,14,18]
+<strong>Output:</strong> 3
+<strong>Explanation</strong>:<strong> </strong>The longest subsequence that is fibonacci-like: [1,11,12], [3,11,14] or [7,11,18].</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>3 &lt;= arr.length &lt;= 1000</code></li>
+	<li><code>1 &lt;= arr[i] &lt; arr[i + 1] &lt;= 10<sup>9</sup></code></li>
+</ul>

0905-length-of-longest-fibonacci-subsequence/solution.py

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+# Approach 1: Brute Force
+
+# M = largest number in arr
+# Time: O(n^2 log M)
+# Space: O(n)
+
+class Solution:
+    def lenLongestFibSubseq(self, arr: List[int]) -> int:
+        num_set = set(arr)
+        max_len = 0
+        n = len(arr)
+
+        for start in range(n):
+            for next in range(start + 1, n):
+                prev = arr[next]
+                curr = arr[start] + arr[next]
+                curr_len = 2
+
+                while curr in num_set:
+                    prev, curr = curr, curr + prev
+                    curr_len += 1
+                    max_len = max(max_len, curr_len)
+
+        return max_len
+