01.两数之和

# 解法一:暴力解法
class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        result = []
        for i in range(len(nums)):
            for j in range(i+1, len(nums)):
                if target == nums[i] + nums[j]:
                    result.append(i)
                    result.append(j)
        return result
     
 
# 解法二：哈希map
class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        result = {}
        for index, value in enumerate(nums):
            if result.get(target-value) is not None:
                return [index, result.get(target-value)]
            result[value] = index
        return result
       
# 注：enumerate() 函数用于将一个可遍历的数据对象(如列表、元组或字符串)组合为一个索引序列，同时列出数据和数据下标，一般用在 for 循环当中。

解法一：
func twoSum(nums []int, target int) []int {
    for i := 0;i<len(nums);i++ {
        for j:=i+1;j<len(nums);j++ {
            if target == nums[i] + nums[j] {
                return []int{i,j}
            }
        }
    }
    return nil
}
时间复杂度：O(N^2)

解法二：
func twoSum(nums []int, target int) []int {
    hashmap := map[int]int{}
    for index, value := range nums {
        if p, ok := hashmap[target-value]; ok {
            return []int{index,p}
        }
        hashmap[value] = index
    }
    return nil
}