【leetcode】1. 两数之和

• Python代码
• • 哈希查找
  • 暴力破解
• 总结

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        hashmap={}
        for index,num in enumerate(nums):
            another_num=target-num
            if another_num in hashmap:
                return [hashmap[another_num],index]
            hashmap[num]=index
        return None

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        for i in range(len(nums)):
            for j in range(len(nums)):
                if nums[i]+nums[j] == target and i != j :
                    return [i,j]
        return None

1、使用字典便于查找和添加。哈希查找复杂度为O(1)，相较于暴力破解效率更高。
2、题目关键在于，能否意识到将两数相减添加到字典中，便于以后查找的操作。