001-eetcode算法实现之两数之和 twoSum | python & golang实现

# -- coding: utf-8 --

• https://leetcode-cn.com/problems/two-sum/solution/liang-shu-zhi-he-by-leetcode-solution/
  """
  给定一个整数数组 nums 和一个整数目标值 target，请你在该数组中找出 和为目标值 target  的那 两个 整数，并返回它们的数组下标。

你可以假设每种输入只会对应一个答案。但是，数组中同一个元素在答案里不能重复出现。

示例:
输入：nums = [2,7,11,15], target = 9
输出：[0,1]
解释：因为 nums[0] + nums[1] == 9 ，返回 [0, 1]

"""

python

# 蛮力枚举 时间O(n2), 空间O(1)
def twoSum1(nums, target):
    """
    :param nums: int[]
    :param target: int
    :return: int[]
    """
    if len(nums) < 2:
        return False

    n = len(nums)
    for i in range(n):
        for j in range(i+1, n):
            if nums[i] + nums[j] == target:
                return [i, j]

    return False

# 哈希表辅助 时间O(n), 空间借助hash表，O(n)
def twoSum(nums, target):
    """
    :param nums: int[]
    :param target: int
    :return: int[] or False
    """
    if len(nums) < 2:
        return False

    hashtable = dict()
    for i,num in enumerate(nums):
        if target-num in hashtable:
            return [hashtable[target - num], i]
        hashtable[num] = i

    return False


if __name__ == "__main__":

    # 蛮力枚举测试用例
    nums1 = []
    target1 = 5
    print(twoSum1(nums1, target1)) # False
    nums2 = [1]
    print(twoSum1(nums2, target1)) # False
    nums3 = [1, 3, 5, 6]
    print(twoSum1(nums3, target1)) # False
    nums4 = [2, 5, 6, 8, 13, 3, 23]
    print(twoSum1(nums4, target1))

    print('*'*50)

    # 哈希表辅助测试用例
    nums1 = []
    target1 = 5
    print(twoSum(nums1, target1))  # False
    nums2 = [1]
    print(twoSum(nums2, target1))  # False
    nums3 = [1, 3, 5, 6]
    print(twoSum(nums3, target1)) # False
    nums4 = [2, 5, 6, 8, 13, 3, 23]
    print(twoSum(nums4, target1))

golang

package main

import "fmt"

func main() {
	var nums = []int{1, 3, 4, 5, 2}
	var target int = 5
	res1 := twoSum1(nums, target)
	fmt.Print(res1)
	fmt.Println()
	res := twoSum(nums, target)
	fmt.Print(res)
}

// 暴力法
func twoSum1(nums []int, target int) []int {
	for i, num := range nums {
		for j := i + 1; j < len(nums); j++ {
			if num+nums[j] == target {
				return []int{i, j}
			}
		}
	}
	return nil
}

// 哈希法
func twoSum(nums []int, target int) []int {
	hashtable := map[int]int{}
	for i, x := range nums {
		if p, ok := hashtable[target-x]; ok {
			return []int{p, i}
		}
		hashtable[x] = i
	}
	return nil
}