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Add_445.java
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Add_445.java
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import java.util.Stack;
public class Add_445 {
public static class ListNode {
int val;
ListNode next;
ListNode(int x) {
val = x;
}
}
// Use stack to reverse linkedlist
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
Stack<Integer> s1 = new Stack<>();
Stack<Integer> s2 = new Stack<>();
while (l1 != null) {
s1.push(l1.val);
l1 = l1.next;
}
while (l2 != null) {
s2.push(l2.val);
l2 = l2.next;
}
// Online solution
/*
int sum = 0;
ListNode head = new ListNode(0);
while (!s1.empty() || !s2.empty()) {
if (!s1.empty()) sum += s1.pop();
if (!s2.empty()) sum += s2.pop();
head.val = sum % 10;
sum /= 10;
ListNode newHead = new ListNode(sum);
newHead.next = head;
head = newHead;
}
return head.val == 0 ? head.next : head;
*/
// My version
int sum = 0;
ListNode dummy = new ListNode(0);
while (!s1.empty() || !s2.empty() || sum > 0) {
if (!s1.empty()) sum += s1.pop();
if (!s2.empty()) sum += s2.pop();
ListNode tmp = new ListNode(sum % 10);
sum /= 10;
tmp.next = dummy.next;
dummy.next = tmp;
}
return dummy.next;
}
}