added: longest consecutive sequence

14. Questions/leetcode 128 - longest consecutive sequence.py

@@ -0,0 +1,22 @@
+# longest consecutive sequence | leetcode 128 | https://leetcode.com/problems/longest-consecutive-sequence/
+# set to look-up previous and next numbers; nested while loop is O(2n)
+
+class Solution:
+ def longestConsecutive(self, nums: list[int]) -> int:
+ if nums == []:
+ return 0
+
+ all = set(nums)
+ longest = 0
+
+ for each in all:
+ if each - 1 not in all:
+ curr = each
+ seq = 1
+ while curr + 1 in all:
+ seq += 1
+ curr = curr + 1
+ if seq > longest:
+ longest = seq
+
+ return longest