2_Add Two Number

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一、题目

题目描述：

传入2个链表，比如2->4->3其实表示的是342，5->6->4其实表示的是465，将2个链表相加，也就是342+465=807，然后将807反转为链表7->0->8。其实就是大数相加问题。

二、解决

思路：通过2个链表同时扫描，用大数相加的方法，c表示进位，num表示当前的值，从头扫描到最后

public ListNode addTwoNumbers2(ListNode l1, ListNode l2) {int num = l1.val + l2.val;int c = 0;if (num > 9){    c = num / 10;    num %= 10;} ListNode current = new ListNode(num);ListNode result = current;l1 = l1.next;l2 = l2.next;while (l1!=null && l2!=null){num = l1.val + l2.val + c;if (num > 9){c = num / 10;num %= 10;} else {c = 0;}ListNode temp = new ListNode(num);current.next = temp;current = current.next;l1 = l1.next;l2 = l2.next;}while (l1 != null){num = l1.val + c;if (num > 9){c = num / 10;num %= 10;} else {c = 0;}ListNode temp = new ListNode(num);current.next = temp;current = current.next;l1 = l1.next;} while (l2 != null){num = l2.val + c;if (num > 9){c = num / 10;num %= 10;} else {c = 0;}ListNode temp = new ListNode(num);current.next = temp;current = current.next;l2 = l2.next;}if (c != 0){ListNode temp = new ListNode(c);current.next = temp;current = current.next;}return result;    }

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