题解 | #链表相加(二)#

BM11 链表相加(二)

/*
 * function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */

/**
 *
 * @param head1 ListNode类
 * @param head2 ListNode类
 * @return ListNode类
 */
function addInList(head1, head2) {
  // write code here
  //   先倒序两个链表
  let reHead1 = reverseList(head1);
  let reHead2 = reverseList(head2);
  let head = new ListNode(0);
  let sumHead = head;
  //   是否有进位
  let exceed = 0;
  //   循环相加倒序后的链表（也就是从个位开始加）
  //   记录是否有进位并相加进位

  while (reHead1 || reHead2) {
    sumHead.next = new ListNode(0);
    const val1 = parseInt(reHead1 ? reHead1.val : 0);
    const val2 = parseInt(reHead2 ? reHead2.val : 0);
    const sum = val1 + val2 + exceed;
    if (sum >= 10) {
      sumHead.next.val = sum % 10;
      exceed = 1;
    } else {
      sumHead.next.val = sum;
      exceed = 0;
    }

    reHead1 = reHead1 ? reHead1.next : null;
    reHead2 = reHead2 ? reHead2.next : null;
    sumHead = sumHead.next;
  }
  //   有进位就再加一个进位
  if (exceed) {
    sumHead.next = new ListNode(exceed);
  }
  //   最后将新链表翻转
  const reSum = reverseList(head.next);
  return reSum;
}

function reverseList(head) {
  let prev = null;
  let curr = head;
  while (curr) {
    [curr.next, curr, prev] = [prev, curr.next, curr];
  }
  return prev;
}

module.exports = {
  addInList: addInList,
};

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