Create longest-arithmetic-sequence.py

Author: kamyu104

Python/longest-arithmetic-sequence.py

@@ -0,0 +1,17 @@
+# Time:  O(n^2)
+# Space: O(n^2)
+
+import collections
+
+class Solution(object):
+    def longestArithSeqLength(self, A):
+        """
+        :type A: List[int]
+        :rtype: int
+        """
+        dp = collections.defaultdict(int)
+        for i in xrange(len(A)-1):
+            for j in xrange(i+1, len(A)):
+                v =  A[j]-A[i]
+                dp[v, j] = max(dp[v, j], dp[v, i]+1)
+        return max(dp.values())+1