LeetCode之Swift

1.Two Sum (Easy)

时间复杂度对O(n^2)
func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
        for i in 0 ..< nums.count {
            for j in i + 1 ..< nums.count {
                let result = nums[i] + nums[j]
                if result == target {
                    return [i, j]
                }
            }
        }
        return [-1, -1]
    }

时间复杂度O(n)
func twoSum_3(_ nums: [Int], _ target: Int) -> [Int] {
        var numberIndexDict = [Int:Int]()
        
        for (index, num) in nums.enumerated() {
            guard let pairedIndex = numberIndexDict[target - num] else {
                numberIndexDict[num] = index
                continue
            }
            
            return [pairedIndex, index]
        }
        
        return [-1, -1]
    }