题解 | #两个链表生成相加链表#

把链表转化呢为数组,然后大数加法

public class Solution {
    /**
     * 
     * @param head1 ListNode类 
     * @param head2 ListNode类 
     * @return ListNode类
     */
    public ListNode addInList (ListNode head1, ListNode head2) {
        // write code here
        // 把两个链表分别保存到ArrayList 里面,然后执行大数字加法
        ArrayList<Integer> num1 = new ArrayList<>();
        ArrayList<Integer> num2 = new ArrayList<>();
        while(head1 != null){
            num1.add(head1.val);
            head1 = head1.next;
        }
        while(head2 != null){
            num2.add(head2.val);
            head2 = head2.next;
        }
        // 初始化sum 数组
        int sumLen = Math.max(num1.size(),num2.size())+1;
        int sumIndex = sumLen -1;
        int[] sum = new int[sumLen];
        for(int i =0; i < sumLen; i++){
            sum[i] = 0;
        }
        int num1Index =num1.size()-1,num2Index = num2.size()-1;
        while(num1Index >=0 && num2Index >=0){
            // 求和
            int summ = num1.get(num1Index--) + num2.get(num2Index--) + sum[sumIndex];
            // 求该位的值
            sum[sumIndex--] = summ % 10;
            // 求进位
            sum[sumIndex] = summ / 10;
        }
        while(num1Index >=0){
            int summ = num1.get(num1Index--) + sum[sumIndex];
            // 求该位的值
            sum[sumIndex--] = summ % 10;
            // 求进位
            sum[sumIndex] = summ / 10;
        }
        while(num2Index >=0){
            int summ = num2.get(num2Index--) + sum[sumIndex];
            // 求该位的值
            sum[sumIndex--] = summ % 10;
            // 求进位
            sum[sumIndex] = summ / 10;
        }
        // 把求出来的和拼接为一个链表
        if(sum[0] == 0){
            ListNode returnHead = new ListNode(1);
            ListNode p = returnHead;
            for(int j = 1; j<sumLen; j++){
                p.next = new ListNode(sum[j]);
                p = p.next;
            }
            return returnHead.next;
        }else{
            ListNode returnHead = new ListNode(1);
            ListNode p = returnHead;
            for(int j = 0; j< sumLen; j++){
                p.next = new ListNode(sum[j]);
                p = p.next;
            }
            return returnHead.next;
        }
    }
}