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564. Find the Closest Palindrome

Description

Given a string n representing an integer, return the closest integer (not including itself), which is a palindrome. If there is a tie, return the smaller one.

The closest is defined as the absolute difference minimized between two integers.

 

Example 1:

Input: n = "123"
Output: "121"

Example 2:

Input: n = "1"
Output: "0"
Explanation: 0 and 2 are the closest palindromes but we return the smallest which is 0.

 

Constraints:

  • 1 <= n.length <= 18
  • n consists of only digits.
  • n does not have leading zeros.
  • n is representing an integer in the range [1, 1018 - 1].

Solutions

Solution 1

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class Solution:
    def nearestPalindromic(self, n: str) -> str:
        x = int(n)
        l = len(n)
        res = {10 ** (l - 1) - 1, 10**l + 1}
        left = int(n[: (l + 1) >> 1])
        for i in range(left - 1, left + 2):
            j = i if l % 2 == 0 else i // 10
            while j:
                i = i * 10 + j % 10
                j //= 10
            res.add(i)
        res.discard(x)

        ans = -1
        for t in res:
            if (
                ans == -1
                or abs(t - x) < abs(ans - x)
                or (abs(t - x) == abs(ans - x) and t < ans)
            ):
                ans = t
        return str(ans)

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class Solution {
    public String nearestPalindromic(String n) {
        long x = Long.parseLong(n);
        long ans = -1;
        for (long t : get(n)) {
            if (ans == -1 || Math.abs(t - x) < Math.abs(ans - x)
                || (Math.abs(t - x) == Math.abs(ans - x) && t < ans)) {
                ans = t;
            }
        }
        return Long.toString(ans);
    }

    private Set<Long> get(String n) {
        int l = n.length();
        Set<Long> res = new HashSet<>();
        res.add((long) Math.pow(10, l - 1) - 1);
        res.add((long) Math.pow(10, l) + 1);
        long left = Long.parseLong(n.substring(0, (l + 1) / 2));
        for (long i = left - 1; i <= left + 1; ++i) {
            StringBuilder sb = new StringBuilder();
            sb.append(i);
            sb.append(new StringBuilder(i + "").reverse().substring(l & 1));
            res.add(Long.parseLong(sb.toString()));
        }
        res.remove(Long.parseLong(n));
        return res;
    }
}

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class Solution {
public:
    string nearestPalindromic(string n) {
        long x = stol(n);
        long ans = -1;
        for (long t : get(n))
            if (ans == -1 || abs(t - x) < abs(ans - x) || (abs(t - x) == abs(ans - x) && t < ans))
                ans = t;
        return to_string(ans);
    }

    unordered_set<long> get(string& n) {
        int l = n.size();
        unordered_set<long> res;
        res.insert((long) pow(10, l - 1) - 1);
        res.insert((long) pow(10, l) + 1);
        long left = stol(n.substr(0, (l + 1) / 2));
        for (long i = left - 1; i <= left + 1; ++i) {
            string prefix = to_string(