LeetCode 445. Add Two Numbers II (两数相加 II)
题目标签:Linked List
题目给了我们两个 数字的linked list,让我们把它们相加,返回一个新的linked list。
因为题目要求不能 reverse,可以把 两个list 的数字都 存入 两个stack。利用了stack的特性,就可以从后面把数字相加,具体看code。
Java Solution:
Runtime: 6 ms, faster than 51.06%
Memory Usage: 45.4 MB, less than 64.71%
完成日期:07/08/2019
关键点:stack
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ class Solution { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { Stack<Integer> s1 = new Stack<Integer>(); Stack<Integer> s2 = new Stack<Integer>(); // store two numbers into stacks while(l1 != null) { s1.push(l1.val); l1 = l1.next; } while(l2 != null) { s2.push(l2.val); l2 = l2.next; } // adding two numbers from stacks int sum = 0; ListNode list = new ListNode(0); while(!s1.empty() || !s2.empty()) { if(!s1.empty()) sum += s1.pop(); if(!s2.empty()) sum += s2.pop(); list.val = sum % 10; // get the value ListNode head = new ListNode(sum / 10); // get the carry head.next = list; list = head; sum /= 10; } // need to check if the head is 0 or not return list.val == 0 ? list.next : list; } }
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