題目描述

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sumas a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

• Example 1:
  

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

• Example 2:

Input: l1 = [0], l2 = [0]
Output: [0]

• Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

給定兩個連結串列，每個連結串列倒序儲存著數字，兩個數字求和，返回新的連結串列。

java解法

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;
  }

  static ListNode of(int[] nums) {
    ListNode dummyHead = new ListNode(-1);
    for (int i = nums.length - 1; i >= 0; i--) {
      dummyHead.next = new ListNode(nums[i], dummyHead.next);
    }
    return dummyHead.next;
  }

  @Override
  public String toString() {
    ListNode cur = this;
    StringBuilder buffer = new StringBuilder();
    while (cur != null) {
      buffer.append(cur.val).append("->");
      cur = cur.next;
    }
    return buffer.toString();
  }
}
 

class Solution {

  public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    ListNode curL1 = l1;
    ListNode curL2 = l2;
    //進位
    int carry = 0;
    ListNode dummyHead = new ListNode(-1);
    ListNode cur = dummyHead;
    while (curL1 != null || curL2 != null) {
      int val1 = curL1 == null ? 0 : curL1.val;
      int val2 = curL2 == null ? 0 : curL2.val;
      int val = val1 + val2 + carry;
      cur.next = new ListNode(val % 10);
      carry = val / 10;
      if (curL1 != null) {
        curL1 = curL1.next;
      }
      if (curL2 != null) {
        curL2 = curL2.next;
      }
      cur = cur.next;
    }
    if (carry == 1) {
      cur.next = new ListNode(1);
    }
    return dummyHead.next;
  }


  public static void main(String[] args) {
    ListNode l1 = ListNode.of(new int[]{9, 9, 9, 9, 9, 9, 9});
    ListNode l2 = ListNode.of(new int[]{9, 9, 9, 9});
    ListNode listNode = new Solution().addTwoNumbers(l1, l2);
    System.out.println(l1);
    System.out.println(l2);
    System.out.println(listNode);
  }
}