【HOT100】DAY1

秃头狂魔2026-03-31 8:59

两数之和

哈希，不在哈希表就先存起来

python 复制代码

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        hash_map = {}
        for idx, num in enumerate(nums):
            a = target - num
            if a in hash_map:
                return [hash_map[a], idx]
            hash_map[num] = idx
        return []

字母异位词分组

哈希，用排序后的字符串作分类指标

"".join(sorted(s))：先将s转换成字符列表并排序，之后数据类型转回字符串，作为key

python 复制代码

class Solution:
    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
        from collections import defaultdict

        hash_map = defaultdict(list)
        for s in strs:
            key = "".join(sorted(s))
            hash_map[key].append(s)
        return list(hash_map.values())

最长连续序列

if num - 1 not in num_set：集合中搜索，集合原生支持 x in s，平均时间复杂度 O(1)

python 复制代码

class Solution:
    def longestConsecutive(self, nums: List[int]) -> int:
        num_set = set(nums)
        max_length = 0
        for num in num_set:
            if num - 1 not in num_set:
                current_num = num
                current_length = 1
                while current_num + 1 in num_set:
                    current_num += 1
                    current_length += 1
                max_length = max(max_length, current_length)
        return max_length

移动零

前指针自循环，若不指向0则后指针跟着前指针走，若指向0则后指针不动，等到前指针不指向0了，再将0换到后面。像一个会"收集0"的滑动窗口，等前指针到头了，则0也收集完了。

python 复制代码

class Solution:
    def moveZeroes(self, nums: List[int]) -> None:
        """
        Do not return anything, modify nums in-place instead.
        """
        j = 0
        for i in range(len(nums)):
            if nums[i] != 0:
                nums[i], nums[j] = nums[j], nums[i]
                j += 1