Merge pull request neetcode-gh#70 from Pegasus02K/patch-5

Create 128-Longest-Consecutive-Sequence.cpp

Author: neetcode-gh

cpp/128-Longest-Consecutive-Sequence.cpp

@@ -0,0 +1,21 @@
+class Solution {
+public:
+	int longestConsecutive(vector<int>& nums) {
+		unordered_set<int> hs;
+		for (int n : nums) {
+			hs.insert(n);
+		}
+
+		int longest = 0;
+		for (int n : nums) {
+			// if n-1 is not in the set, the element can be the start of a sequence
+			if (hs.find(n - 1) == hs.end()) {
+				int length = 1;
+				while (hs.find(n + length) != hs.end())
+					++length;
+				longest = max(longest, length);
+			}
+		}
+		return longest;
+	}
+};