CCI 2.5 链表整数求和

package test;

import java.util.Stack;

public class AddLinkedInt {
	
	//两个整数反向存放
	//即，个位排在链表的首部
	public Node addLinkedInt(Node l1, Node l2){
		
		Node newHead = new Node(0);
		Node tail = newHead;
		int carry = 0;
		Node p1 = l1, p2 = l2;
		while(p1!=null || p2!=null){
			int val1 = (p1==null)? 0 : p1.val;
			int val2 = (p2==null)? 0 : p2.val;
			int val = (val1+val2+carry)%10;
			carry = (val1+val2+carry)/10;
			tail.next = new Node(val);
			tail = tail.next;
		}
		if(carry != 0)
			tail.next = new Node(carry);
		return newHead.next;
	}
	
	//两个整数正向存放
	//即，个位排在链表的末尾
	public Node addLinkedInt(Node l1, Node l2){
		//这里要借助栈来处理
		Stack<Integer> st1 = new Stack<Integer>();
		Stack<Integer> st2 = new Stack<Integer>();
		Node p1=l1, p2=l2;
		//将两链表的数据分别压入栈中
		while(p1 != null){
			st1.push(p1.val);
			p1 = p1.next;
		}
		while(p2 != null){
			st2.push(p2.val);
			p2 = p2.next;
		}
		//将结果相加入栈
		Stack<Integer> res = new Stack<Integer>();
		int carry=0;
		while( !st1.empty() || !st2.empty()){
			int val1 = st1.empty() ? 0 : st1.pop();
			int val2 = st2.empty() ? 0 : st2.pop();
			res.push((val1+val2+carry)%10);
			carry = (val1+val2+carry)/10;
		}
		if(carry != 0)//注意进位的处理
			res.push(carry);
		Node newHead = new Node(0);
		Node tail = newHead;
		while(!res.empty()){
			tail.next = new Node(res.pop());
			tail = tail.next;
		}
		return newHead.next;	
	}
}