[LeetCode]Add Two Numbers II
2016-11-08 16:41
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Question
You are given two linked lists representing two non-negative numbers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
Example:
本题难度Medium。
stack法
【复杂度】
时间 O(N) 空间 O(N)
【思路】
本题与两个Array相加那题非常相似,但是链表可不是能从后往前读取的,那么就用stack。
【注意】
我本来想在某个input链表上进行修改的(这样是可以的,如果超出了链表头就new ListNode),不过为保持代码干净就不这么写(这样也会对input产生side effect,在工程应用会对client造成一定干扰,不利于函数式编程)。
【代码】
You are given two linked lists representing two non-negative numbers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
Example:
Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 8 -> 0 -> 7
本题难度Medium。
stack法
【复杂度】
时间 O(N) 空间 O(N)
【思路】
本题与两个Array相加那题非常相似,但是链表可不是能从后往前读取的,那么就用stack。
【注意】
我本来想在某个input链表上进行修改的(这样是可以的,如果超出了链表头就new ListNode),不过为保持代码干净就不这么写(这样也会对input产生side effect,在工程应用会对client造成一定干扰,不利于函数式编程)。
【代码】
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ public class Solution { public ListNode addTwoNumbers(ListNode l1, ListNode l2) { //require ListNode ans=null; Stack<ListNode> stack1=new Stack<ListNode>(),stack2=new Stack<ListNode>(); //invariant while(l1!=null||l2!=null){ if(l1!=null){ stack1.push(l1); l1=l1.next; } if(l2!=null){ stack2.push(l2); l2=l2.next; } } int a=0,b=0,carry=0,sum=0; while(!stack1.isEmpty()||!stack2.isEmpty()){ if(!stack1.isEmpty()) a=stack1.pop().val; else a=0; if(!stack2.isEmpty()) b=stack2.pop().val; else b=0; sum=a+b+carry; ListNode tmp=new ListNode(sum%10); tmp.next=ans; ans=tmp; carry=sum/10; } if(carry!=0){ ListNode tmp=new ListNode(carry); tmp.next=ans; ans=tmp; } //ensure return ans; } }
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