feat:add Solution.cpp for 0128.Longest Consecutive Sequence (doocs#331)

Author: Stackingrule

solution/0100-0199/0128.Longest Consecutive Sequence/Solution.cpp

@@ -0,0 +1,16 @@
+class Solution {
+public:
+    int longestConsecutive(vector<int>& nums) {
+        int res = 0;
+        unordered_set<int> set{nums.begin(), nums.end()};
+        for (int num : nums) {
+            if (!set.count(num)) continue;
+            set.erase(num);
+            int pre = num - 1, next = num + 1;
+            while (set.count(pre)) set.erase(pre--);
+            while (set.count(next)) set.erase(next++);
+            res = max(res, next - pre - 1);
+        }
+        return res;
+    }
+};