Create 564. Find the Closest Palindrome

564. Find the Closest Palindrome

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+class Solution {
+public:
+    string nearestPalindromic(string n) {
+        if(n.length()==1)
+            return to_string(stoi(n)-1);
+
+        int d = n.length();
+        vector<long> candidates;
+        candidates.push_back(pow(10,d-1)-1);
+        candidates.push_back(pow(10,d)+1);
+
+        int mid = (d+1)/2;
+        long prefix = stol(n.substr(0,mid));
+        vector<long> v = {prefix,prefix+1, prefix-1};
+        for(long i : v)
+        {
+            string postfix = to_string(i);
+            if(d%2!=0)
+                postfix.pop_back();
+            reverse(postfix.begin(), postfix.end());
+            string c = to_string(i)+postfix;
+            candidates.push_back(stol(c));
+        }
+        long mindiff = LONG_MAX;
+        long result;
+        long num = stol(n);
+        for(int i=0;i<5;i++)
+        {
+            if(candidates[i]!=num && abs(candidates[i]-num)<mindiff)
+            {
+                mindiff = abs(candidates[i]-num);
+                result = candidates[i];
+            }
+            else if(abs(candidates[i]-num)==mindiff)
+                result = min(result, candidates[i]);
+        }
+        return to_string(result);
+    }
+};