dfs, corrected from above

1625. Lexicographically Smallest String After Applying Operations Medium.cpp

@@ -65,6 +65,59 @@ class Solution {
     }
 };
 
+//dfs, corrected from above
+//Runtime: 592 ms, faster than 29.07% of C++ online submissions for Lexicographically Smallest String After Applying Operations.
+//Memory Usage: 169.2 MB, less than 5.03% of C++ online submissions for Lexicographically Smallest String After Applying Operations.
+class Solution {
+public:
+    int n;
+    unordered_set<string> visited;
+    unordered_map<string, string> memo;
+
+    string add(string& s, int a){
+        string ret = s;
+        for(int i = 1; i < n; i+=2){
+            ret[i] = '0'+(ret[i]-'0'+a)%10;
+        }
+        return ret;
+    }
+
+    string rotate(string& s, int b){
+        string ret = s;
+
+        ret = s.substr(b) + s.substr(0, b);
+
+        return ret;
+    }
+
+    string dfs(string& s, int& a, int& b){
+        if(memo.find(s) != memo.end()){
+            // cout << "memo" << endl;
+            return memo[s];
+        }else if(visited.find(s) != visited.end()){
+            //to jump out of the loop!
+            return "aaaa";
+        }else{
+            visited.insert(s);
+            string sadd = add(s, a);
+            string srot = rotate(s, b);
+
+            // cout << s << ", add: " << sadd << ", rot: " << srot << endl;
+
+            memo[s] = min({s, dfs(sadd, a, b), dfs(srot, a, b)});
+
+            // cout << s << " -> " << memo[s] << endl;
+            return memo[s];
+        }
+    }
+
+    string findLexSmallestString(string s, int a, int b) {
+        n = s.size();
+
+        return dfs(s, a, b);
+    }
+};
+
 //dfs
 //https://leetcode.com/problems/lexicographically-smallest-string-after-applying-operations/discuss/899489/Basic-DFS-Brute-force-or-This-kind-of-questions-DFS
 //no early stop make it correct?