[Swift]LeetCode633. 平方数之和 | Sum of Square Numbers

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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

---

给定一个非负整数 c ，你要判断是否存在两个整数 a 和 b，使得 a2 + b2 = c。

示例1:

输入: 5
输出: True
解释: 1 * 1 + 2 * 2 = 5 

示例2:

输入: 3
输出: False

---

Runtime: 8 ms

Memory Usage: 19 MB

class Solution {
    func judgeSquareSum(_ c: Int) -> Bool {
        var a:Int = 0
        var b:Int = Int(sqrt(Double(c)))
        while (a <= b)
        {
            if a * a + b * b == c
            {
                return true
            }
            else if a * a + b * b < c
            {
                a += 1
            }
            else
            {
                b -= 1
            }
        }
        return false
    }
}

---

8ms

class Solution {
    func judgeSquareSum(_ c: Int) -> Bool {
        var c = c; var i = 2
        while (i*i <= c) {
            var multi = 0
            if (c % i == 0) {
                while (c % i == 0) {
                    multi += 1
                    c /= i
                }
                if (i % 4 == 3 && multi % 2 != 0) {
                    return false
                }
            }
            i += 1
        }
        return c % 4 != 3
    }
}

---

12ms

class Solution {
    func judgeSquareSum(_ c: Int) -> Bool {
        var left = 0
        var right: Int = Int(sqrt(Double.init(exactly: c)!))
        while left <= right {
            let cur = left*left + right*right
            if cur == c {
                return true
            }

            if cur < c {
                left += 1
            } else {
                right -= 1
            }
        }
        return false
    }
}

---

24ms

class Solution {
  func judgeSquareSum(_ c: Int) -> Bool {
    let root = Int(sqrt(Double(c)))
    
    for i in 0...root {
      let diff = c - i * i
      let diffRoot = sqrt(Double(diff))
      
      if Double(Int(diffRoot)) == diffRoot {
        return true
      }
    }
    
    return false
  }
}

---

28ms

class Solution {
    func judgeSquareSum(_ c: Int) -> Bool {
        for a in 0...Int(sqrt(Double(c))) {
            let b = Int(sqrt(Double(c - a * a)))
            if a * a + b * b == c {
                return true
            }
        }
        return false
    }
}