Create find-lucky-integer-in-an-array.cpp

Author: kamyu104

C++/find-lucky-integer-in-an-array.cpp

@@ -0,0 +1,25 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    int findLucky(vector<int>& arr) {
+        const auto& count = counter(arr);
+        int result = -1;
+        for (const auto& [k, v] : count) {
+            if (k == v) {
+                result = max(result, k);
+            }
+        }
+        return result;
+    }
+
+private:
+    unordered_map<int, int> counter(const vector<int>& arr) {
+        unordered_map<int, int> count;
+        for (const auto& i : arr) {
+            ++count[i];
+        }
+        return count;
+    }
+};