LeetCode_One question per day_python_ The sum of two numbers for the first question

Python writes an algorithm problem every day

first day

Question: Given an integer array nums and a target value target, please find the two integers whose sum is the target value in the array and return their array subscripts.

You can assume that each input will only correspond to one answer. However, the same element in the array cannot be used twice.

 

Source: LeetCode
Link: https://leetcode-cn.com/problems/two-sum

1. Brute force algorithm 

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        for i in range(0, len(nums)):
            for j in range(i + 1, len(nums)):
                if nums[i] + nums[j] == target:
                    return [i, j]
        return[]

2. Use dictionary to simulate hash solution

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        hashmap = {}
        for ind, num in enumerate(nums):
            hashmap[num] = ind
            #   hashmap = {(2,0),(7,1),(11,2),(15,3)}
        for i, num in enumerate(nums):
             j = hashmap.get(target - num)
            #   j : 2 7 None None
             if j is not None and i != j:
                return [i, j]