create 0187-repeated-dna-sequences.cpp

cpp/0187-repeated-dna-sequences.cpp

@@ -0,0 +1,21 @@
+class Solution {
+public:
+    vector<string> findRepeatedDnaSequences(string s) {
+
+        int n = s.size();
+        if(n <=10){ return {};}
+        vector<string> answer;
+
+        unordered_map<string,int> hash;
+
+        for(int i = 0;i<=s.size()-10;i++){
+            string ss = s.substr(i,10);
+            hash[ss]++;
+            if(hash[ss]==2){
+                answer.push_back(ss);
+            }
+        }
+
+        return answer;
+    }
+};