1027_Longest_Arithmetic_Sequence

Author: Partho Biswas

README.md

@@ -701,6 +701,7 @@ BFS, DFS, Dijkstra, Floyd–Warshall, Bellman-Ford, Kruskal, Prim's, Minimum Spa
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 |50| **[140. Word Break II](https://tinyurl.com/yb9yotou)** | [Python](https://tinyurl.com/wu6rdaw/140_Word_Break_II.py), [Swift](https://tinyurl.com/wuja3c4/140_Word_Break_II.swift)| [Art 1](https://tinyurl.com/yc9jvbpl), [Art 2](https://tinyurl.com/yaa7b7lu) | Hard | **OHH Boy, you must recheck this, Important. TODO: Check again.  An unique combination of DP, DFS and Backtracking** |
+|51| **[1027. Longest Arithmetic Sequence](https://tinyurl.com/y7w7mmfn)** | [Python](https://tinyurl.com/wu6rdaw/1027_Longest_Arithmetic_Sequence.py), [Swift](https://tinyurl.com/wuja3c4/1027_Longest_Arithmetic_Sequence.swift)| [Art 1](https://tinyurl.com/ycto2x5o), [Art 2](https://tinyurl.com/yab7byj5) | Medium | **I didn't know that map can be used in 1d bottom-up dp. learned new things** |
 
 
 </p>

leetcode.com/python/1027_Longest_Arithmetic_Sequence.py

@@ -0,0 +1,30 @@
+from collections import defaultdict
+
+
+class Solution(object):
+    def longestArithSeqLength(self, A):
+        """
+        :type A: List[int]
+        :rtype: int
+        """
+        dp = defaultdict(lambda: 1)  # setting the default value of defaultdict to 1
+        for i in range(len(A)):
+            for j in range(i + 1, len(A)):
+                ai, aj = A[i], A[j]
+                dp[j, aj - ai] = dp[i, aj - ai] + 1
+        return max(dp.values())
+
+
+"""
+[9,4,7,2,10]  >> [4,7,10]
+
+ j>
+i 9,4,7,2,10
+V
+9   x   
+4     x    
+7       x
+2         x
+10          x 
+
+"""