LeetCode Blind 75 in Swift: Solving the "Two Sum" Problem

LeetCode Blind 75 in Swift: Solving the "Two Sum" Problem

Problem: Two Sum

The Two Sum problem is one of the most popular problems on LeetCode. Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to the target. You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Input: nums = [2, 7, 11, 15], target = 9
Output: [0, 1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].

Swift Solution

class Solution {
    func twoSum(_ nums: [Int], _ target: Int) -> [Int] {
        var numDict = [Int: Int]()
        for (index, num) in nums.enumerated() {
            let complement = target - num
            if let complementIndex = numDict[complement] {
                return [complementIndex, index]
            }
            numDict[num] = index
        }
        return []
    }
}

let solution = Solution()
let nums = [2, 7, 11, 15]
let target = 9
let result = solution.twoSum(nums, target)
print(result) // Output: [0, 1]

Explanation

This solution uses a dictionary to store each element’s index as it traverses the array. For each number, we compute its complement (i.e., target - num), and if the complement is already in the dictionary, we return the indices. Otherwise, we store the current number and its index.

Comments

Post a Comment

Popular posts from this blog

LeetCode Blind 75 in Swift: Solving the "Find Minimum in Rotated Sorted Array" Problem

Problem: Find Minimum in Rotated Sorted Array The Find Minimum in Rotated Sorted Array problem asks you to find the minimum element in a rotated sorted array of unique elements. Example: Input: nums = [3, 4, 5, 1, 2] Output: 1 Explanation: The minimum value is 1. Swift Solution class Solution { func findMin(_ nums: [Int]) -> Int { var left = 0 var right = nums.count - 1 while left nums[right] { left = mid + 1 } else { right = mid } } return nums[left] } } let solution = Solution() let nums = [3, 4, 5, 1, 2] let result = solution.findMin(nums) print(result) // Output: 1 Explanation This problem can be solved efficiently using binary search. The rotated sorted array has two sorted halves. By comparing the middle element with the rightmost element, we can determine which ha...
Read more

LeetCode Blind 75 in Swift: Solving the "3Sum" Problem

Problem: 3Sum The 3Sum problem asks you to find all unique triplets in the array that give the sum of zero. Each triplet should be listed only once, even if multiple combinations can produce the same triplet. Example: Input: nums = [-1, 0, 1, 2, -1, -4] Output: [[-1, -1, 2], [-1, 0, 1]] Explanation: The two triplets with sum zero are [-1, -1, 2] and [-1, 0, 1]. Swift Solution class Solution { func threeSum(_ nums: [Int]) -> [[Int]] { let nums = nums.sorted() var result = [[Int]]() for i in 0.. 0 && nums[i] == nums[i - 1] { continue } var left = i + 1 var right = nums.count - 1 while left Explanation In this solution, the array is first sorted, which helps in efficiently finding triplets that sum to zero. For each element, we use the two-pointer technique to find pairs that together with the ...
Read more

LeetCode Blind 75 in Swift: Solving the "Product of Array Except Self" Problem

Problem: Product of Array Except Self The Product of Array Except Self problem asks you to return an array answer such that answer[i] is equal to the product of all the elements of nums except nums[i] . Example: Input: nums = [1, 2, 3, 4] Output: [24, 12, 8, 6] Swift Solution class Solution { func productExceptSelf(_ nums: [Int]) -> [Int] { let n = nums.count var answer = Array(repeating: 1, count: n) var leftProduct = 1 for i in 0.. Explanation In this solution, we first calculate the product of all elements to the left of each element and store it in the answer array. Then, we calculate the product of all elements to the right of each element and multiply it with the corresponding value in the answer array. This approach avoids division and runs in O(n) time.
Read more