- Partition Array for Maximum Sum
1877. Minimize Maximum Pair Sum in Array
Source: https://leetcode.com/problems/minimize-maximum-pair-sum-in-array/
Difficulty: Medium
func minPairSum(_ nums: [Int]) -> Int {
let halfCount = (nums.count+1)/2
let num = nums.sorted()
let firstHalf = num[0..<halfCount].sorted()
let secondHalf = num[halfCount..<nums.count].sorted(by: >)
var temp = [Int]()
for i in 0..<halfCount {
temp.append(firstHalf[i] + secondHalf[i])
}
return temp.max()!
}1823. Find the Winner of the Circular Game
Source: https://leetcode.com/problems/find-the-winner-of-the-circular-game/
Difficulty: Medium
func findTheWinner(_ n: Int, _ k: Int) -> Int {
var arr = Array(1...n)
if k == 1 {
return arr[arr.count-1]
} else {
while arr.count != 1 {
for i in 1...(k-1) {
arr.append(arr.removeFirst())
}
arr.removeFirst()
}
}
return arr[0]
}347. Top K Frequent Elements
Source: https://leetcode.com/problems/top-k-frequent-elements/
Difficulty: Medium
func topKFrequent(_ nums: [Int], _ k: Int) -> [Int] {
var dict = [Int:Int]()
var result: [Int] = []
for i in nums {
dict[i, default: 0] += 1
}
let sorted = dict.sorted { $0.1 > $1.1 }
for i in 0..<k {
result.append(sorted[i].key)
}
return result
}49. Group Anagrams
Source: https://leetcode.com/problems/group-anagrams/
Difficulty: Medium
func groupAnagrams(_ strs: [String]) -> [[String]] {
var temp = [String: [String]]()
for i in 0..<strs.count {
let mytemp = String(strs[i].sorted())
temp[mytemp, default: []] += [strs[i]]
}
return Array(temp.values)
}215. Kth Largest Element in an Array
Source: https://leetcode.com/problems/kth-largest-element-in-an-array/
Difficulty: Medium
func findKthLargest(_ nums: [Int], _ k: Int) -> Int {
let sortedArray = nums.sorted(by: >)
return sortedArray[k-1]
}781. Rabbits in Forest
Source: https://leetcode.com/problems/rabbits-in-forest/
Difficulty: Medium
func numRabbits(_ answers: [Int]) -> Int {
var setForDictKey = Set(answers)
var result = 0
var dict = [(Int, Int)]()
for i in setForDictKey {
let count = answers.filter { $0 == i }.count
dict.append((i, count))
}
for i in dict {
result += i.1 / (i.0 + 1) * (i.0 + 1)
if i.1 % (i.0 + 1) > 0 {
result += i.0 + 1
} else {
}
}
return result
}189. Rotate Array
Source: https://leetcode.com/problems/rotate-array/
Difficulty: Medium
func rotate(_ nums: inout [Int], _ k: Int) {
if k % nums.count > 0 {
for i in 1...(k % nums.count) {
nums.insert(nums.removeLast(), at: 0)
}
} else if nums.count == 1 {
} else if k % nums.count == 0 {
} else {
}
}1551. Minimum Operations to Make Array Equal
Source: https://leetcode.com/problems/minimum-operations-to-make-array-equal/
Difficulty: Medium
func minOperations(_ n: Int) -> Int {
var arr = [Int]()
for i in 0...(n - 1) {
arr.append(2 * i + 1)
}
var result = 0
if arr.count % 2 == 0 {
let middleInd = arr.count / 2
let target = (arr[middleInd] + arr[middleInd - 1]) / 2
for i in arr[middleInd...] {
result += i - target
}
} else if arr.count % 2 == 1 {
let middleInd = arr.count / 2
let target = arr[middleInd]
for i in arr[(middleInd + 1)...] {
result += i - target
}
}
return result
}442. Find All Duplicates in an Array
Source: https://leetcode.com/problems/find-all-duplicates-in-an-array/
Difficulty: Medium
// Solution 1
func findDuplicates(_ nums: [Int]) -> [Int] {
var dict = [Int:Int]()
var result = [Int]()
for i in nums {
dict[i, default: 0] += 1
}
for (key, value) in dict {
if value > 1 {
result.append(key)
}
}
return result
}
// Solution 2
func findDuplicates(_ nums: [Int]) -> [Int] {
let sorted = nums.sorted(by: < )
var left = 0
var right = 1
var result = [Int]()
while right < sorted.count {
if sorted[left] == sorted[right] {
result.append(sorted[right])
}
left += 1
right += 1
}
return result
}260. Single Number III
Source: https://leetcode.com/problems/single-number-iii/
Difficulty: Medium
func singleNumber(_ nums: [Int]) -> [Int] {
var dict = [Int:Int]()
var result = [Int]()
for i in nums {
dict[i, default: 0] += 1
}
for (key, value) in dict {
if value == 1 {
result.append(key)
}
}
return result
}1780. Check if Number is a Sum of Powers of Three
Source: https://leetcode.com/problems/check-if-number-is-a-sum-of-powers-of-three/
Difficulty: Medium
func checkPowersOfThree(_ n: Int) -> Bool {
var origin = n
var temp = [Int]()
while origin != 0 {
temp.append(origin % 3)
origin = origin / 3
}
return !temp.contains(2)
}137. Single Number II
Source: https://leetcode.com/problems/single-number-ii/
Difficulty: Medium
func singleNumber(_ nums: [Int]) -> Int {
var dict = [Int:Int]()
var result = Int()
for i in nums {
dict[i, default: 0] += 1
}
for (key, value) in dict {
if value == 1 {
result = key
}
}
return result
}912. Sort an Array
Source: https://leetcode.com/problems/sort-an-array/
Difficulty: Medium
func sortArray(_ nums: [Int]) -> [Int] {
return nums.sorted(by: < )
}1492. The kth Factor of n
Source: https://leetcode.com/problems/the-kth-factor-of-n/
Difficulty: Medium
func kthFactor(_ n: Int, _ k: Int) -> Int {
var temp = [Int]()
for i in 1...n {
if n % i == 0 {
temp.append(i)
}
}
if temp.count > k - 1 {
return temp[k - 1]
} else {
return -1
}
}451. Sort Characters By Frequency
Source: https://leetcode.com/problems/sort-characters-by-frequency/
Difficulty: Medium
func frequencySort(_ s: String) -> String {
var dict = [Character:Int]()
for i in s {
dict[i, default: 0] += 1
}
let sorted = dict.sorted{ $0.1 > $1.1 }
var result = ""
for (key, value) in sorted {
for i in 1...value {
result.append(key)
}
}
return result
}