Create longest-palindrome-by-concatenating-two-letter-words.cpp

Author: kamyu104

C++/longest-palindrome-by-concatenating-two-letter-words.cpp

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+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    int longestPalindrome(vector<string>& words) {
+        unordered_map<string, int> cnt;
+        for (const auto& x : words) {
+            ++cnt[x];
+        }
+        int result = 0, remain = 0;
+        for (const auto& [x, c] : cnt) {
+            const string mirror(crbegin(x), crend(x));
+            if (x == mirror) {
+                result += c / 2;
+                remain |= c % 2;
+            } else if (x < mirror && cnt.count(mirror)) {
+                result += min(c, cnt[mirror]);
+            }
+        }
+        return result * 4 + remain * 2;
+    }
+};