Create lexicographically-smallest-equivalent-string.cpp

Author: kamyu104

C++/lexicographically-smallest-equivalent-string.cpp

@@ -0,0 +1,43 @@
+// Time:  O(nlog*n) ~= O(n), n is the length of S
+// Space: O(n)
+
+class Solution {
+public:
+    string smallestEquivalentString(string A, string B, string S) {
+        UnionFind union_find(26);
+        for (int i = 0; i < A.length(); ++i) {
+            union_find.union_set(A[i] - 'a', B[i] - 'a');
+        }
+        string result;
+        for (int i = 0; i < S.length(); ++i) {
+            const auto& parent = union_find.find_set(S[i] - 'a');
+            result.push_back(parent + 'a');
+        }
+        return result;
+    }
+    
+private:
+    class UnionFind {
+    public:
+        UnionFind(const int n) : set_(n) {
+            iota(set_.begin(), set_.end(), 0);
+        }
+        
+        int find_set(const int x) {
+           if (set_[x] != x) {
+               set_[x] = find_set(set_[x]);  // Path compression.
+           }
+           return set_[x];
+        }
+
+        void union_set(const int x, const int y) {
+            int x_root = find_set(x), y_root = find_set(y);
+            if (x_root != y_root) {
+                set_[max(x_root, y_root)] = min(x_root, y_root);
+            }
+        }
+
+    private:
+        vector<int> set_;
+    };
+};