added longest_consecutive_sequence TheAlgorithms#9436

Author: JehanPatel

other/longest_consecutive_sequence.py

@@ -0,0 +1,36 @@
+# Longest Consecutive Sequence
+# https://www.github.com/JehanPatel
+
+# Logic behind the question
+
+# nums = [2, 3, 1, 4, 5]
+# 1. num = 2
+#    1 is present -> Don't run the inner loop
+# 2. num = 3
+#    2 is present -> Don't run the inner loop
+# 3. curr_num = 1
+#    0 is not present -> Run the inner loop
+#    a. curr_num = 1, curr_len = 1, while condition: True
+#    b. curr_num = 2, curr_len = 2, while condition: True
+#    c. curr_num = 3, curr_len = 3, while condition: True
+#    d. curr_num = 4, curr_len = 4, while condition: True
+#    e. curr_num = 5, curr_len = 5, while condition: False
+
+# Optimal Code
+
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        max_len = 0
+        num_set = set(nums)
+        for num in nums:
+            if num - 1 not in num_set:
+                curr_num = num
+                curr_len = 1
+                while curr_num + 1 in num_set:
+                    curr_num += 1
+                    curr_len += 1
+                max_len = max(max_len, curr_len)
+        return max_len
+    
+# Time and Space complexity = o(n)    
+# refer to leetcode discussion tab for further clarification.