add: 220705

cpp/2207/220705.cpp

@@ -0,0 +1,25 @@
+#include <unordered_set>
+#include <vector>
+
+/**
+ * 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.
+ */
+
+class Solution {
+public:
+	int longestConsecutive(const std::vector<int>& nums) {
+		std::unordered_set<int> s(nums.begin(), nums.end());
+		int ans = 0;
+		for (int i : s) {
+			if (s.count(i - 1))
+				continue;
+			int cur = i, ca = 1;
+			for (; s.count(1 + cur); ++cur)
+				++ca;
+			ans = std::max(ans, ca);
+		}
+		return ans;
+	}
+};