Create find-the-closest-palindrome.cpp

Author: kamyu104

C++/find-the-closest-palindrome.cpp

@@ -0,0 +1,30 @@
+// Time:  O(l)
+// Space: O(l)
+
+class Solution {
+public:
+    string nearestPalindromic(string n) {
+        const auto l = n.size();
+        vector<long long> candidates;
+        candidates.emplace_back(static_cast<long long>(pow(10, l)) + 1);
+        candidates.emplace_back(static_cast<long long>(pow(10, l - 1)) - 1);
+        auto prefix = stol(n.substr(0, (l + 1) / 2));
+        for (long long i = -1; i <= 1; ++i) {
+            auto p = to_string(prefix + i);
+            auto pp = p + string(p.rbegin() + (l % 2), p.rend());
+            candidates.emplace_back(stol(pp));
+        }
+        long long num = stol(n), closest_val = numeric_limits<long long>::max();
+        for (const auto& val : candidates) {
+            if (val == num) {
+                continue;
+            }
+            if (abs(val - num) < abs(closest_val - num)) {
+                closest_val = val;
+            } else if (abs(val - num) == abs(closest_val - num)) {
+                closest_val = min(closest_val, val);
+            }
+        }
+        return to_string(closest_val);
+    }
+};