Create ransom-note.cpp

Author: kamyu104

C++/ransom-note.cpp

@@ -0,0 +1,22 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    bool canConstruct(string ransomNote, string magazine) {
+        vector<int> counts(26);
+        int letters = 0;
+        for (const auto& c : ransomNote) {
+            if (counts[c - 'a']++ == 0) {
+                ++letters;
+            }
+        }
+        for (const auto& c : magazine) {
+            if (--counts[c - 'a'] == 0 && --letters == 0) {
+                // Break as soon as possible if letters have been enough.
+                break;
+            }
+        }
+        return letters == 0;
+    }
+};