_564.java

/**
 * LeetCode 564 - Find the Closest Palindrome
 * <p>
 * A tricky problem...
 * The basic idea is to break the palindrome and slightly modify the left half.
 * The logic of code can be dramatically simplified by considering more cases.
 */
public class _564 {

    long ans = 0, diff = Long.MAX_VALUE, n = 0;

    private void update(String val) {
        try {
            long tmp = Long.parseLong(val);
            if (tmp == n) return;
            if (Math.abs(tmp - n) < diff || (Math.abs(tmp - n) == diff && tmp < ans)) {
                ans = tmp;
                diff = Math.abs(tmp - n);
            }
        } catch (Exception e) {
        }
    }

    private void concat(long leftHalf) {
        String s = "" + leftHalf, rs = new StringBuilder(s).reverse().toString();
        update(s + rs);
        update(s + rs.substring(1));
    }

    public String nearestPalindromic(String n) {
        this.n = Long.parseLong(n);
        diff = Long.MAX_VALUE;
        long leftHalf = Long.parseLong(n.substring(0, (n.length() + 1) / 2));
        concat(leftHalf - 1);
        concat((leftHalf - 1) * 10 + 9); // Handle 1, 1000, 100000, etc.
        concat(leftHalf);
        concat(leftHalf + 1);
        concat((leftHalf + 1) / 10); // Handle 9, 999, 99999, etc.
        return "" + ans;
    }
}