Leetcode刷题指南Java(每日更新)

两数之和https://leetcode-cn.com/problems/two-sum

//暴力枚举 
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];
     }
 }

//哈希表
class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map hashtable = new HashMap();
        for (int i = 0; i < nums.length; ++i) {
            if (hashtable.containsKey(target - nums[i])) {
                return new int[]{hashtable.get(target - nums[i]), i};
            }
            hashtable.put(nums[i], i);
        }
        return new int[0];
    }
}

合并两个有序链表https://leetcode-cn.com/problems/merge-two-sorted-lists/ 

class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if(l1==null){
            return l2;
        }else if(l2 == null){
            return l1;
        }else if(l1.val < l2.val){
            l1.next = mergeTwoLists(l1.next,l2);
            return l1;
        }else{
            l2.next = mergeTwoLists(l2.next,l1);
            return l2;
        }

    }
}