[Swift]LeetCode202. 快乐数 | Happy Number

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Write an algorithm to determine if a number is "happy".

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

编写一个算法来判断一个数是不是“快乐数”。

一个“快乐数”定义为：对于一个正整数，每一次将该数替换为它每个位置上的数字的平方和，然后重复这个过程直到这个数变为 1，也可能是无限循环但始终变不到 1。如果可以变为 1，那么这个数就是快乐数。

示例: 

输入: 19
输出: true
解释: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

---

8ms

class Solution {
    func isHappy(_ n: Int) -> Bool {
        var fast = n
        var slow = n
        fast = sumOfSquares(fast)
        fast = sumOfSquares(fast)
        slow = sumOfSquares(slow)
        while fast != slow {
            fast = sumOfSquares(fast)
            fast = sumOfSquares(fast)
            slow = sumOfSquares(slow) 
        }
        return slow == 1
        
    }
    
    func sumOfSquares(_ n: Int) -> Int {
        var num = n
        var sum = 0
        while num > 0 {
            let value = num%10
            sum += value*value
            num /= 10
        }
        return sum
    }
}

---

12ms

class Solution {
    func isHappy(_ n: Int) -> Bool {
        var hasOccurredMap = Dictionary<Int, Bool>()
        return isHappy(n, &hasOccurredMap)
    }
    
    private func isHappy(
        _ n: Int,
        _ hasOccurredMap: inout Dictionary<Int, Bool>) -> Bool {
        guard n != 1 else { return true }
        guard hasOccurredMap[n] == nil else { return false }
        var m = 0
        var temp = n
        while temp > 0 {
            let digit = temp % 10
            temp /= 10
            m += digit * digit
        }
        hasOccurredMap[n] = true
        return isHappy(m, &hasOccurredMap)
    }
}

---

12ms

class Solution {
    func isHappy(_ n: Int) -> Bool {
      var nT = n
        
        while (nT != 1 && nT != 4) {
            var t = 0
            while (nT>0) {
                t += (nT % 10) * (nT % 10)
                nT /= 10
            }
            nT = t
        }
        return nT == 1  
    }
}

---

16ms

class Solution {
    private let map:[Character: Int] = ["0" : 0, "1" : 1, "2": 2, "3": 3, "4": 4, "5": 5, "6": 6, "7": 7, "8": 8, "9": 9]
    private var memory = Set<Int>()
    
    func isHappy(_ n: Int) -> Bool {
        var digits = getDigits(n)
        var square = getSquare(digits)
        memory.insert(square)
        if square == 1 {
            return true
        } else {
            while true {
                digits = getDigits(square)
                square = getSquare(digits)
                if memory.contains(square) {
                    return false
                }
                memory.insert(square)
                if square == 1 {
                    return true
                }
            }
        }
        return true
    }
    
    func getDigits(_ n: Int) -> [Int] {
        var digits = [Int]()
        for s in String(n) {
            guard let val = map[s] else {
                continue
            }
            digits.append(val)
        }
        return digits
    }
    
    func getSquare(_ digits: [Int]) -> Int {
        var res = 0
        for digit in digits {
            res += digit * digit
        }
        return res
    }
}

---

20ms

class Solution {
    func isHappy(_ n: Int) -> Bool {
        var prevSums: Set<Int> = Set()
        var curr = n
        while curr != 1 {
            if prevSums.contains(curr) {
                return false
            }
            prevSums.insert(curr)
            let digits: [Int] = String(curr).compactMap { Int(String($0)) }
            var newSum = 0
            for digit in digits {
                newSum += (digit * digit)
            }
            curr = newSum
        }
        return true
    }
}

---

24ms

class Solution {
    func isHappy(_ n: Int) -> Bool {
        var preciuslySeen: [Int: Bool] = [:]
        
        var check = n
        while(check != 1) {
            var digits = String(check).characters

            let squares = digits.map { ( Int(String($0)) ?? 0 ) * ( Int(String($0)) ?? 0 ) }
            let sum = squares.reduce(0) { $0 + $1 }

            if sum == 1 { 
                return true
            } else if preciuslySeen[sum] == true {
                return false
            }

            preciuslySeen[sum] = true
            check = sum
        }
        
        return true
    }
}