[Swift]LeetCode523. 连续的子数组和 | Continuous Subarray Sum

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Given a list of non-negative numbers and a target integer k, write a function to check if the array has a continuous subarray of size at least 2 that sums up to the multiple of k, that is, sums up to n*k where n is also an integer.

Example 1:

Input: [23, 2, 4, 6, 7],  k=6
Output: True
Explanation: Because [2, 4] is a continuous subarray of size 2 and sums up to 6. 

Example 2:

Input: [23, 2, 6, 4, 7],  k=6
Output: True
Explanation: Because [23, 2, 6, 4, 7] is an continuous subarray of size 5 and sums up to 42. 

Note:

1. The length of the array won't exceed 10,000.
2. You may assume the sum of all the numbers is in the range of a signed 32-bit integer.

---

给定一个包含非负数的数组和一个目标整数 k，编写一个函数来判断该数组是否含有连续的子数组，其大小至少为 2，总和为 k 的倍数，即总和为 n*k，其中 n 也是一个整数。

示例 1:

输入: [23,2,4,6,7], k = 6
输出: True
解释: [2,4] 是一个大小为 2 的子数组，并且和为 6。

示例 2:

输入: [23,2,6,4,7], k = 6
输出: True
解释: [23,2,6,4,7]是大小为 5 的子数组，并且和为 42。

说明:

1. 数组的长度不会超过10,000。
2. 你可以认为所有数字总和在 32 位有符号整数范围内。

---

192ms

class Solution {
    func checkSubarraySum(_ nums: [Int], _ k: Int) -> Bool {
        var map = [Int: Int]()
        map[0] = -1
        var runningSum = 0
        for i in 0..<nums.count {
            runningSum += nums[i]
            if k != 0 {
                runningSum %= k
            }
            let pre = map[runningSum]
            if pre != nil {
                if (i - pre!) > 1 { return true}
            } else {
                map[runningSum] = i
            }
        }
        return false
    }
}

---

232ms

class Solution {
    func checkSubarraySum(_ nums: [Int], _ k: Int) -> Bool {
        if nums.count < 2 { return false }       
        if (k == 0) { return nums[0] == 0 && nums[1] == 0 }
        var dict = [Int:Int]()
        
        var sum = 0
        for i in 0...nums.count-1 {
            sum += nums[i]
            
            let r = sum % k 
            if r == 0 { 
                
                if(i>=1) {
                    
                    return true
                }
            }
            if let value = dict[r] {
                if (i - value >= 2) { return true }
            }
            else {
                dict[r] = i
            }
            
            
        }
        return false
    }
}

---

316ms

class Solution {
    func isMultiple(_ num: Int, _ k: Int) -> Bool {
        if k == 0 {
            return num == 0
        } else {
            return num % k == 0
        }
    }
    func checkSubarraySum(_ nums: [Int], _ k: Int) -> Bool {
        var preSum: [Int] = []
        for (i, num) in nums.enumerated() {
            let sum = (preSum.last ?? 0) + num
            preSum.append(sum)
            if i >= 1 && isMultiple(sum, k) {
                return true
            }
        }
        if 0 > nums.count - 2 {
            return false
        }
        for i in 0..<(nums.count - 2) {
            for j in (i + 2)..<nums.count {
                let sum = preSum[j] - preSum[i]
                if isMultiple(sum, k) {
                    return true
                }
            }
        }
        return false
    }
}

---

324ms

class Solution {
    func checkSubarraySum(_ nums: [Int], _ k: Int) -> Bool {
        var nums = nums
        let count = nums.count
        guard count > 1 else {
            return false
        }
        for i in 1..<count {
            nums[i] += nums[i - 1]
        }
        
        for i in 1..<count {
            if (k != 0 && nums[i] % k == 0) || (k == 0 && nums[i] == 0) {
                return true
            }
            for j in i + 1..<count {
                if (k != 0 && (nums[j] - nums[j - i - 1]) % k == 0)
                    || (k == 0 && nums[j] - nums[j - i - 1] == 0) {
                    return true
                }
            }
        }
        return false
    }
}

---

340ms

class Solution {
    func checkSubarraySum(_ nums: [Int], _ k: Int) -> Bool {
        var sum: [Int] = []
        var total = 0
        for i in 0..<nums.count {
            total += nums[i]
            sum.append(total)
        }
        
        for start in 0..<nums.count-1 {
            for end in start+1..<nums.count {
                let summ = sum[end] - sum[start] + nums[start]
                if summ == k || (k != 0 && summ%k == 0) {
                    return true
                }
            }
        }
        
        return false
    }
}

---

380ms

class Solution {
    func checkSubarraySum(_ nums: [Int], _ k: Int) -> Bool {
    return checkSubarraySumRecursion(nums, k)
}

func checkSubarraySumRecursion(_ nums : [Int], _ k : Int)->Bool{
    guard nums.count > 1 else{
        return false
    }
    
    var sum : Int = nums[0]
    for index in 1..<nums.count{
        sum += nums[index]
        if k == 0 && sum == 0{
            return true
        }
        
        if k != 0 && sum % k == 0{
            return true
        }
    }
    
    return checkSubarraySumRecursion(Array(nums[1...]), k)
  }
}