给定两个链表，每个链表表示一个非负整数，其各位数字逆序存储在链表的每个节点中。将这两个整数相加，并以相同形式返回一个表示和的链表。
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode() {} * ListNode(int val) { this.val = val; } * ListNode(int val, ListNode next) { this.val = val; this.next = next; } * } */ class Solution { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { // 将l1中数字转换成一个整数 int n1 = 0, m = 1; while(l1 != null){ n1 += l1.val * m; l1 = l1.next; m *= 10; } // 将l2中数字转换成一个整数 int n2 = 0; m = 1; while(l2 != null){ n2 += l2.val * m; l2 = l2.next; m *= 10; } // 两数相加 int sum = n1 + n2; // 将结果按要求转换成链表 ListNode head = null, tail = null; while(sum != 0){ if(head == null){ head = tail = new ListNode(); tail.val = sum % 10; sum /= 10; }else{ tail.next = new ListNode(); tail = tail.next; tail.val = sum % 10; sum /= 10; } } if (tail == null) { // 考虑 0 + 0 == 0 的特殊情况 tail = new ListNode(); tail.val = 0; tail.next = null; head = tail; }else { tail.next = null; } return head; } }
错误原因：使用整型变量记录链表所表示的非负整数的值，将两个整数相加，得到的结果再按题目要求转换成链表形式。这种思路虽然很笨，但对于1568个测试用例中的792个都是可行的，但随着测试用例中整数的位数增多，整数变量会超出范围，导致出现错误结果。尝试使用java.math.BigInteger类，但好像也不可行。
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode() {} * ListNode(int val) { this.val = val; } * ListNode(int val, ListNode next) { this.val = val; this.next = next; } * } */ class Solution { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { int sum = 0, carry = 0; int m = 0, n = 0; ListNode head = null, tail = null; while(l1!= null || l2 != null){ m = l1 == null ? 0 : l1.val; n = l2 == null ? 0 : l2.val; sum = m + n + carry; if (head == null) { head = tail = new ListNode(sum % 10); }else { tail.next = new ListNode(sum % 10); tail = tail.next; } carry = sum / 10; if (l1 != null) { l1 = l1.next; } if (l2 != null) { l2 = l2.next; } } if (carry > 0) { tail.next = new ListNode(carry); tail = tail.next; tail.next = null; } return head; } }
原文：https://www.cnblogs.com/wangmengdx/p/15144600.html