[Swift]LeetCode633. 平方數之和 | Sum of Square Numbers

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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Given a non-negative integer c, your task is to decide whether there're two integers a and b such that a2 + b2 = c.

Example 1:

Input: 5
Output: True
Explanation: 1 * 1 + 2 * 2 = 5 

Example 2:

Input: 3
Output: False

---

給定一個非負整數 c ，你要判斷是否存在兩個整數 a 和 b，使得 a2 + b2 = c。

示例1:

輸入: 5
輸出: True
解釋: 1 * 1 + 2 * 2 = 5 

示例2:

輸入: 3
輸出: False

---

Runtime: 8 ms

Memory Usage: 19 MB

 1 class Solution {
 2     func judgeSquareSum(_ c: Int) -> Bool {
 3         var a:Int = 0
 4         var b:Int = Int(sqrt(Double(c)))
 5         while (a <= b)
 6         {
 7             if a * a + b * b == c
 8             {
 9                 return true
10             }
11             else if a * a + b * b < c
12             {
13                 a += 1
14             }
15             else
16             {
17                 b -= 1
18             }
19         }
20         return false
21     }
22 }

---

8ms

 1 class Solution {
 2     func judgeSquareSum(_ c: Int) -> Bool {
 3         var c = c; var i = 2
 4         while (i*i <= c) {
 5             var multi = 0
 6             if (c % i == 0) {
 7                 while (c % i == 0) {
 8                     multi += 1
 9                     c /= i
10                 }
11                 if (i % 4 == 3 && multi % 2 != 0) {
12                     return false
13                 }
14             }
15             i += 1
16         }
17         return c % 4 != 3
18     }
19 }

---

12ms

 1 class Solution {
 2     func judgeSquareSum(_ c: Int) -> Bool {
 3         var left = 0
 4         var right: Int = Int(sqrt(Double.init(exactly: c)!))
 5         while left <= right {
 6             let cur = left*left + right*right
 7             if cur == c {
 8                 return true
 9             }
10 
11             if cur < c {
12                 left += 1
13             } else {
14                 right -= 1
15             }
16         }
17         return false
18     }
19 }

---

24ms

 1 class Solution {
 2   func judgeSquareSum(_ c: Int) -> Bool {
 3     let root = Int(sqrt(Double(c)))
 4     
 5     for i in 0...root {
 6       let diff = c - i * i
 7       let diffRoot = sqrt(Double(diff))
 8       
 9       if Double(Int(diffRoot)) == diffRoot {
10         return true
11       }
12     }
13     
14     return false
15   }
16 }

---

28ms

 1 class Solution {
 2     func judgeSquareSum(_ c: Int) -> Bool {
 3         for a in 0...Int(sqrt(Double(c))) {
 4             let b = Int(sqrt(Double(c - a * a)))
 5             if a * a + b * b == c {
 6                 return true
 7             }
 8         }
 9         return false
10     }
11 }