两个单链表生成相加链表II

package 链式APlusB;

class ListNode {
int val;
ListNode next = null;

ListNode(int val) {
this.val = val;
}
}

public class Plus {

public static void main(String[] args) {
ListNode one = new ListNode(9);
ListNode two = new ListNode(3);
ListNode three = new ListNode(7);
ListNode four = new ListNode(6);
ListNode five = new ListNode(3);
one.next = two;
two.next = three;
four.next = five;
//print(new Plus().reverse(one));
new Plus().plusAB(one, four);
}

private static void print(ListNode root) {
if (root == null)
return;
System.out.print(root.val + " ");
print(root.next);
}

public ListNode plusAB(ListNode a, ListNode b) {
// write code here
//  a = reverse(a);
//  b = reverse(b);
ListNode ans = null;
//  ListNode aHead = a;
//  ListNode bHead = b;
int add = 0;
while (a != null || b != null) {
int val = 0;
val += add;
if (a != null) {
val += a.val;
a = a.next;
}
if (b != null) {
val += b.val;
b = b.next;
}
if (val > 9) {
add = val / 10;
val %= 10;

if (ans == null) {
ans = new ListNode(val);
} else {
ListNode tmp = ans;
ans = new ListNode(val);
ans.next = tmp;
}
} else {
add = 0;
if (ans == null) {
ans = new ListNode(val);
} else {
ListNode tmp = ans;
ans = new ListNode(val);
ans.next = tmp;
}
}
}
if(add != 0){
ListNode tmp = ans;
ans = new ListNode(add);
ans.next = tmp;
}
//aHead = reverse(aHead);
//bHead = reverse(bHead);
ans = reverse(ans);
return ans;
}

private ListNode reverse(ListNode a) {
ListNode pre = null;
ListNode next = null;
ListNode cur = a;
while (cur != null) {
next = cur.next;
cur.next = pre;
pre = cur;
cur = next;
}
return pre;
}

}