problem 128, longest consecutive sequence

python/problem_128/README.md

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+# 128. Longest Consecutive Sequence
+
+Given an unsorted array of integers nums, return the length of the longest consecutive elements sequence.
+
+You must write an algorithm that runs in O(n) time.
+
+ 
+
+Example 1:
+
+Input: nums = [100,4,200,1,3,2]
+Output: 4
+Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.
+
+Example 2:
+
+Input: nums = [0,3,7,2,5,8,4,6,0,1]
+Output: 9
+
+ 
+
+Constraints:
+
+    0 <= nums.length <= 105
+    -109 <= nums[i] <= 109
+
+