Find the Closest Palindrome.java

class Solution {
    static long pow(long base,long exp){
        long ans = 1;
        for(;exp != 0;){
            if((exp & 1) == 1){
                ans *= base;
            }
            base *= base;
            exp >>= 1;
        }
        return ans;
    }
    public String nearestPalindromic(String n) {
        long num = Long.parseLong(n);
        if(num <= 10){
            return String.valueOf(num - 1);
        }
        long comp[] = new long[5];
        comp[0] = pow(10,n.length() - 1) - 1;
        comp[1] = pow(10,n.length()) + 1;
        int mid = (n.length() + 1) / 2;
        long half = Long.parseLong(n.substring(0,mid));
        long pref[] = {half,half + 1,half - 1};
        for(int i = 0;i < 3;i++){
            StringBuilder st = new StringBuilder(String.valueOf(pref[i]));
            if(n.length() % 2 == 1) st.deleteCharAt(st.length() - 1);
            st.reverse();
            comp[i + 2] = Long.parseLong(String.valueOf(pref[i]) + st.toString()); 
        }
        long min = Long.MAX_VALUE;
        long ans = Long.MAX_VALUE;
        for(int i = 0;i < 5;i++){
            long dif = Math.abs(num - comp[i]);
            if(dif != 0 && min > dif){
                min = dif;
                ans = comp[i];
            }
            else if(min == dif) ans = Math.min(ans,comp[i]);
        }
        return String.valueOf(ans);
    }
}