Create freedom-trail.cpp

C++/freedom-trail.cpp

@@ -0,0 +1,30 @@
+// Time:  O(k) ~ O(k * r^2)
+// Space: O(r)
+
+class Solution {
+public:
+    int findRotateSteps(string ring, string key) {
+        unordered_map<char,vector<int>> lookup;
+        for (int i = 0; i < ring.size(); ++i) {
+            lookup[ring[i]].emplace_back(i);
+        }
+        int cnt = 0;
+
+        vector<vector<int>> dp(2, vector<int> (ring.size()));
+        vector<int> tmp(1, 0);
+        vector<int> *prev = &tmp;
+        for (int i = 1; i <= key.size(); ++i) {
+            fill(dp[i % 2].begin(), dp[i % 2].end(), numeric_limits<int>::max());
+            for (const auto& j : lookup[key[i - 1]]) {
+                for (const auto& k : *prev) {
+                    int min_dist = min((k + ring.size() - j) % ring.size(),
+                                       (j + ring.size() - k) % ring.size()) +
+                                   dp[(i - 1) % 2][k];
+                    dp[i % 2][j] = min(dp[i % 2][j], min_dist);
+                }
+            }
+            prev = &lookup[key[i - 1]];
+        }
+        return *min_element(dp[key.size() % 2].begin(), dp[key.size() % 2].end()) + key.size();
+    }
+};