Single Pass, O(1) space Java Simple

[AshesNoobCoder]

public class Solution {
    public ListNode solve(ListNode A) {
        ListNode iter = A;
        ListNode one = A;
        while(iter!=null){
            if(iter.val==0){
                iter.val = one.val;
                one.val = 0;
                one = one.next;
                iter = iter.next;
            }else{
                iter = iter.next;
            }
        }
        return A;
    }
}