LeetCode - 两数相加

题目解析：https://leetcodechina.com/problems/add-two-numbers/description/

https://github.com/biezhihua/LeetCode

核心解析：

1. 链表对应结点相加时增加前一个结点的进位，并保存下一个结点的进位；除法得进位，模得结果。

2. 两个链表长度不一致时，要处理较长链表剩余的高位和进位计算的值；

3. 如果最高位计算时还产生进位，则还需要添加一个额外结点。

最佳解法：

ListNode addTwoNumbers(ListNode l1, ListNode l2) {
ListNode tmp = null;
ListNode result = null;

int carry = 0;
while (l1 != null || l2 != null || carry != 0) {
int sum = (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val) + carry;
carry = sum / 10;

ListNode node = new ListNode(sum % 10);
if (tmp == null) {
tmp = node;
result = tmp;
} else {
tmp.next = node;
tmp = tmp.next;
}

l1 = l1 == null ? null : l1.next;
l2 = l2 == null ? null : l2.next;
}

return result;
}

public class ListNode {
int val;
ListNode next;

ListNode(int x) {
val = x;
}
}

我的解法：

/**
* https://leetcodechina.com/problems/add-two-numbers/description/ */
public class Code_3_4_AddTwoNumbers {

@Test
public void test() {
ListNode _342 = new ListNode(2);
_342.next = new ListNode(4);
_342.next.next = new ListNode(3);

ListNode _465 = new ListNode(5);
_465.next = new ListNode(6);
_465.next.next = new ListNode(4);

ListNode result = addTwoNumbers(_342, _465);
Assert.assertEquals(7, result.val);
Assert.assertEquals(0, result.next.val);
Assert.assertEquals(8, result.next.next.val);

ListNode result1 = addTwoNumbers(new ListNode(5), new ListNode(5));
Assert.assertEquals(0, result1.val);
Assert.assertEquals(1, result1.next.val);

ListNode _98 = new ListNode(9);
_98.next = new ListNode(8);

ListNode _1 = new ListNode(1);
ListNode result2 = addTwoNumbers(_98, _1);
Assert.assertEquals(0, result2.val);
Assert.assertEquals(9, result2.next.val);
}

ListNode addTwoNumbers(ListNode l1, ListNode l2) {
ListNode tmp = null;
ListNode result = null;

boolean flag = false;

while (l1 != null && l2 != null) {

int cur = l1.val + l2.val + (flag ? 1 : 0);

flag = cur >= 10;

ListNode node = new ListNode(flag ? cur % 10 : cur);
if (tmp == null) {
tmp = node;
result = tmp;
} else {
tmp.next = node;
tmp = tmp.next;
}

l1 = l1.next;
l2 = l2.next;
}

while (l1 != null) {

int cur = l1.val + (flag ? 1 : 0);

flag = cur >= 10;

ListNode node = new ListNode(flag ? cur % 10 : cur);
if (tmp == null) {
tmp = node;
result = tmp;
} else {
tmp.next = node;
tmp = tmp.next;
}

l1 = l1.next;

}

while (l2 != null) {

int cur = l2.val + (flag ? 1 : 0);

flag = cur >= 10;

ListNode node = new ListNode(flag ? cur % 10 : cur);
if (tmp == null) {
tmp = node;
result = tmp;
} else {
tmp.next = node;
tmp = tmp.next;
}
l2 = l2.next;
}

if (flag) {
tmp.next = new ListNode(1);
}

return result;
}

public class ListNode {
int val;
ListNode next;

ListNode(int x) {
val = x;
}
}
}