[Swift]LeetCode279. 完全平方数 | Perfect Squares

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Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.

Example 1:

Input: n = 12
Output: 3 
Explanation: 12 = 4 + 4 + 4.

Example 2:

Input: n = 13
Output: 2
Explanation: 13 = 4 + 9.

---

给定正整数 n，找到若干个完全平方数（比如 1, 4, 9, 16, ...）使得它们的和等于 n。你需要让组成和的完全平方数的个数最少。

示例 1:

输入: n = 12
输出: 3 
解释: 12 = 4 + 4 + 4.

示例 2:

输入: n = 13
输出: 2
解释: 13 = 4 + 9.

---

12ms

class Solution {
    func numSquares(_ n: Int) -> Int {
        var n = n
        while n % 4 == 0 {
            n /= 4
        }
        
        if n % 8 == 7 {
            return 4
        }
        
        var a = 0
        while a * a <= n {
            let b = Int(sqrt(Double(n - a * a)))
            if a * a + b * b == n {
                let ca =  a == 0 ? 0 : 1
                let cb = b == 0 ? 0 : 1
                return ca + cb
            }
            a += 1
        }
        
        return 3
    }
}

---

1236ms

class Solution {
    func numSquares(_ n: Int) -> Int {
        var dp: [Int] = [Int](repeating: Int.max, count: n+1)
        dp[0] = 0
        for i in 0...n {
            var j = 1
            while i + j * j <= n {
                dp[i + j * j] = min(dp[i] + 1, dp[i + j * j])
                j += 1
            }
        }
        
        return dp[n]
    }
}

---

1308ms

class Solution {
    func numSquares(_ n: Int) -> Int {
        
        var dp = [Int](repeating: 9223372036854775807, count: n+1)
        dp[0] = 0
        for i in 0...n {
            var j = 1
            while i + j*j <= n {
                dp[i+j*j] = min(dp[i+j*j], dp[i]+1)
                j += 1
            }
        }
        return dp.last ?? 1
        
    }
}

---

1324ms

class Solution {
func numSquares(_ n: Int) -> Int {
    guard n > 0 else {
        return 0
    }
    
    var dp = Array.init(repeating: Int.max, count: n + 1)
    dp[0] = 0
    
    for i in 0...n {
        var j = 1
        while i + j * j <= n {
            dp[i + j * j] = min(dp[i + j * j], dp[i] + 1)
            
            j += 1
        }
    }
    
    return dp[n]
}
}

---

1484ms

class Solution {
    func numSquares(_ n: Int) -> Int {
        var nums = Array(repeating: Int.max, count: n + 1)
        nums[0] = 0
        for index in 0...n {
            var j = 1
            while index + j * j <= n {
                nums[index + j * j] = min(nums[index + j * j], nums[index] + 1)
                j += 1
            }
        }
        return nums.last!
    }
}

---

1596ms

class Solution {
    var times: [Int] = []
    var once: [Int] = []
    var candidates: Set<Int> = Set<Int>()
    
    func createArrs(_ n: Int) {
        times = [Int](repeating:0, count:n+1)
        for i in 1...n {
            times[i] = i
        }

        var cnt = Int(sqrt(Double(n)))
        once = [Int](repeating:0, count:cnt+1)
        for i in 1...cnt {
            times[i*i] = 1
            once[i] = i*i
        }
        
        let once_set = Set(once)
        for i in 1...n {
            candidates.insert(i)
        }
    }
    
    func fillTheTimes(_ curTimes: Int) {
        var preTimes = curTimes - 1
        for i in 1...times.count - 1 {
            if times[i] == preTimes {
                for j in 1...once.count - 1 {
                    if once[j] > i {
                        break
                    }
                    var k = i + once[j]
                    if k > times.count - 1 {
                        break
                    }
                    if times[k] > curTimes {
                        times[k] = curTimes
                    }
                }
            }
        }
    }
    
    func fillAllTimes() {
        var cur_times = 1
        while times[times.count - 1] > cur_times {
            cur_times += 1
            fillTheTimes(cur_times)
        }
    }
    
    func f(_ n: Int) -> Int {
        createArrs(n)
        fillAllTimes()
        return times[n]
    }
    
    func numSquares(_ n: Int) -> Int {
        return f(n)
    }
}