50 lines
1.3 KiB
Swift
50 lines
1.3 KiB
Swift
/**
|
|
* File: two_sum.swift
|
|
* Created Time: 2023-01-03
|
|
* Author: nuomi1 (nuomi1@qq.com)
|
|
*/
|
|
|
|
/* Method one: Brute force enumeration */
|
|
func twoSumBruteForce(nums: [Int], target: Int) -> [Int] {
|
|
// Two-layer loop, time complexity is O(n^2)
|
|
for i in nums.indices.dropLast() {
|
|
for j in nums.indices.dropFirst(i + 1) {
|
|
if nums[i] + nums[j] == target {
|
|
return [i, j]
|
|
}
|
|
}
|
|
}
|
|
return [0]
|
|
}
|
|
|
|
/* Method two: Auxiliary hash table */
|
|
func twoSumHashTable(nums: [Int], target: Int) -> [Int] {
|
|
// Auxiliary hash table, space complexity is O(n)
|
|
var dic: [Int: Int] = [:]
|
|
// Single-layer loop, time complexity is O(n)
|
|
for i in nums.indices {
|
|
if let j = dic[target - nums[i]] {
|
|
return [j, i]
|
|
}
|
|
dic[nums[i]] = i
|
|
}
|
|
return [0]
|
|
}
|
|
|
|
@main
|
|
enum LeetcodeTwoSum {
|
|
/* Driver Code */
|
|
static func main() {
|
|
// ======= Test Case =======
|
|
let nums = [2, 7, 11, 15]
|
|
let target = 13
|
|
// ====== Driver Code ======
|
|
// Method one
|
|
var res = twoSumBruteForce(nums: nums, target: target)
|
|
print("Method one res = \(res)")
|
|
// Method two
|
|
res = twoSumHashTable(nums: nums, target: target)
|
|
print("Method two res = \(res)")
|
|
}
|
|
}
|