LeetCode热题hot100

1. 两数之和

class Solution {
   
    public int[] twoSum(int[] nums, int target) {
   
        int n = nums.length;
        for (int i = 0; i < n; ++i) {
   
            for (int j = i + 1; j < n; ++j) {
   
                if (nums[i] + nums[j] == target) {
   
                    return new int[]{
   i, j};
                }
            }
        }
        return new int[0];
    }
}

2.两数相加

class Solution {
   
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
   
        ListNode head = null, tail = null;//声明一个链表， 给定头、尾结点
        int carry = 0;//进位
        while (l1 != null || l2 != null) {
   
       		 //若没有，默认为0
            int n1 = l1 != null ? l1.val : 0;
            int n2 = l2 != null ? l2.val : 0;
            int sum = n1 + n2 + carry;
			
            if (head == null) {
   //开始时
                head = tail = new ListNode(sum % 10);//尾结点指向头结点
            } else {