Why this solution is AC? An object does not cost extra space?

  • 0
    public class Solution {
        public boolean isPalindrome(int x) {
            StringBuilder sb1=new StringBuilder(Integer.toString(x));//  extra space??
            StringBuilder sb2=new StringBuilder(Integer.toString(x));//  extra space??
            return sb1.toString().equals(sb2.reverse().toString());

    Or does for(int i=0;i<len;i++) cost exra space?

  • 0

    Just a guess, but strings are probably implemented as dynamic arrays since you can append infinitely to them.

  • 0

    Well it most definitely does use extra space but they can't (or at least they don't) test it in the OJ

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