leetcode 2. 两数相加

高精度类

import java.math.BigInteger;


 
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
    	BigInteger a,b;
    	
        ListNode p=l1;
        StringBuilder sb=new StringBuilder();
        while(true)
        {
        	sb.append(p.val);
        	p=p.next;
        	if(p==null)break;
        }

        sb.reverse();
        a=new BigInteger(sb.toString());
        
        p=l2;
        sb.setLength(0);
        while(true)
        {
        	sb.append(p.val);
        	p=p.next;
        	if(p==null)break;
        }
        sb.reverse();
        b=new BigInteger(sb.toString());
        
        a=a.add(b);
        
        ListNode ans=null,tmp;
        
        ans=new ListNode(a.mod(BigInteger.valueOf(10)).intValue(),null);
        a=a.divide(BigInteger.valueOf(10));
        
        tmp=ans;
        
        while(a.compareTo(BigInteger.valueOf(0))!=0)
        {
        	int t=a.mod(BigInteger.valueOf(10)).intValue();
        	a=a.divide(BigInteger.valueOf(10));
        	tmp.next=new ListNode(t,null);
        	tmp=tmp.next;
        }
        return ans;
    }
}

模拟加法

import java.math.BigInteger;


 
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int t,c=0;
        ListNode ans=null,tmp=null;
    	while(l1!=null||l2!=null)
        {
            t=0;
            if(l1!=null)t+=l1.val;
            if(l2!=null)t+=l2.val;
            t+=c;
            if(t>=10)
            {
                c=1;t-=10;
            }
            else c=0;
            if(tmp==null)
            {
                tmp=new ListNode(t,null);
                ans=tmp;
            }
            else{
                tmp.next=new ListNode(t,null);
                tmp=tmp.next;
            }
            if(l1!=null)l1=l1.next;
            if(l2!=null)l2=l2.next;
        }
        if(c!=0)tmp.next=new ListNode(c,null);

        return ans;
        
    }
}