[Swift]LeetCode829. 连续整数求和 | Consecutive Numbers Sum

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Given a positive integer N, how many ways can we write it as a sum of consecutive positive integers?

Example 1:

Input: 5
Output: 2
Explanation: 5 = 5 = 2 + 3

Example 2:

Input: 9
Output: 3
Explanation: 9 = 9 = 4 + 5 = 2 + 3 + 4

Example 3:

Input: 15
Output: 4
Explanation: 15 = 15 = 8 + 7 = 4 + 5 + 6 = 1 + 2 + 3 + 4 + 5

Note: 1 <= N <= 10 ^ 9.

---

给定一个正整数 N，试求有多少组连续正整数满足所有数字之和为 N?

示例 1:

输入: 5
输出: 2
解释: 5 = 5 = 2 + 3，共有两组连续整数([5],[2,3])求和后为 5。

示例 2:

输入: 9
输出: 3
解释: 9 = 9 = 4 + 5 = 2 + 3 + 4

示例 3:

输入: 15
输出: 4
解释: 15 = 15 = 8 + 7 = 4 + 5 + 6 = 1 + 2 + 3 + 4 + 5

说明: 1 <= N <= 10 ^ 9

---

24ms

class Solution {
    func consecutiveNumbersSum(_ N: Int) -> Int {
        let num : CGFloat = CGFloat(N);
        var n : CGFloat  = 1;
        var a : CGFloat = 10;
        var m = 0;
        while (a>=1) {
            a = CGFloat(num/n - (n-1)/2);
            let b : Int = Int(a);
            if (a == CGFloat(b) && a >= 1) {
                m += 1;
            }
            n += 1;
        }
        return m;
    }
}

---

24ms

class Solution {
    func consecutiveNumbersSum(_ N: Int) -> Int {
        var count = 0
        var length = 1
        while 2*N >= length*length + length {
            if (2*N+length-length*length) % (2*length) == 0 {
                count += 1
            }
            length = length + 1
        }
        return count
    }
}

---

Runtime: 32 ms

Memory Usage: 18.4 MB

class Solution {
    func consecutiveNumbersSum(_ N: Int) -> Int {
        var ans:Int = 1
        var i:Int = 2
        while(i * (i + 1) / 2 <= N)
        {
            if (N - i * (i + 1) / 2) % i == 0
            {
                ans += 1
            }
            i += 1
        }
        return ans
    }
}