[Swift]LeetCode658. 找到 K 个最接近的元素 | Find K Closest Elements

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Given a sorted array, two integers k and x, find the kclosest elements to x in the array. The result should also be sorted in ascending order. If there is a tie, the smaller elements are always preferred.

Example 1:

Input: [1,2,3,4,5], k=4, x=3
Output: [1,2,3,4] 

Example 2:

Input: [1,2,3,4,5], k=4, x=-1
Output: [1,2,3,4] 

Note:

1. The value k is positive and will always be smaller than the length of the sorted array.
2. Length of the given array is positive and will not exceed 104
3. Absolute value of elements in the array and x will not exceed 104

UPDATE (2017/9/19):
The arr parameter had been changed to an array of integers(instead of a list of integers). Please reload the code definition to get the latest changes.

---

给定一个排序好的数组，两个整数 k 和 x，从数组中找到最靠近 x（两数之差最小）的 k 个数。返回的结果必须要是按升序排好的。如果有两个数与 x 的差值一样，优先选择数值较小的那个数。

示例 1:

输入: [1,2,3,4,5], k=4, x=3
输出: [1,2,3,4] 

示例 2:

输入: [1,2,3,4,5], k=4, x=-1
输出: [1,2,3,4] 

说明:

1. k 的值为正数，且总是小于给定排序数组的长度。
2. 数组不为空，且长度不超过 104
3. 数组里的每个元素与 x 的绝对值不超过 104 

更新(2017/9/19):
这个参数 arr 已经被改变为一个整数数组（而不是整数列表）。 请重新加载代码定义以获取最新更改。

---

Runtime: 328 ms

Memory Usage: 19.8 MB

class Solution {
    func findClosestElements(_ arr: [Int], _ k: Int, _ x: Int) -> [Int] {
        var left:Int = 0
        var right:Int = arr.count - k
        while(left < right)
        {
            var mid:Int = left + (right - left) / 2
            if x - arr[mid] > arr[mid + k] - x
            {
                left = mid + 1
            }
            else
            {
                right = mid
            }
        }
        return Array(arr[left..<(left + k)])
    }
}

---

336ms

class Solution {
    func findClosestElements(_ arr: [Int], _ k: Int, _ x: Int) -> [Int] {
        if arr.count < 2 {
            return arr
        }
        
        let count = arr.count
        var closest = 0
        var minDiff = Int.max
        var left = 0
        var right = 0
        var result = [Int]()
        
        for i in 0..<count {
            let diff = abs(arr[i] - x)
            if diff < minDiff || arr[i] == x {
                closest = i
                minDiff = diff
            }
        }
        
        left = closest
        right = closest
        while right - left + 1 < k {
            if left - 1 < 0 {
                right += 1
            } else if right + 1 > (count - 1) {
                left -= 1
            } else if abs(x - arr[left - 1]) <= abs(x - arr[right + 1]) {
                left -= 1
            } else {
                right += 1
            }
        }
        
        for i in left...right {
            result.append(arr[i])
        }
        
        return result
    }
}

---

372ms

struct Span {
    var start: Int
    var end: Int
    var mid: Int {
        return start + ((end - start) / 2)
    }
    var inverted: Bool {
        return end < start
    }
    func leftRange() -> Span {
        return Span(start: start, end: mid - 1)
    }
    func rightRange() -> Span {
        return Span(start: mid + 1, end: end)
    }
}


class Solution {
    func findClosestIndex(arr: [Int], x: Int, span: Span) -> Int {
        let mid = span.mid
        
        if mid == arr.count - 1 { return mid }
        if mid <= 0 { return 0 }
        
        let midVal = arr[mid]
        let nextVal = arr[mid + 1]
        if midVal <= x && nextVal >= x {
            return abs(x - midVal) <= abs(x - nextVal) ? mid : mid + 1
        } else if midVal < x {
            return findClosestIndex(arr: arr, x: x, span: span.rightRange())
        } else {
            return findClosestIndex(arr: arr, x: x, span: span.leftRange())
        }
    }
    
    func findClosestElements(_ arr: [Int], _ k: Int, _ x: Int) -> [Int] {
        let startSpan = Span(start: 0, end: arr.count - 1)
        let index = findClosestIndex(arr: arr, x: x, span: startSpan)
        var left = index - 1
        var right = index + 1
        var returnVals: [Int] = [arr[index]]
        for _ in 1..<k {
            let rightVal = right < arr.count ? arr[right] : 10000000
            let leftVal = left >= 0 ? arr[left] : 100000000
            if abs(x - leftVal) <= abs(x - rightVal) {
                returnVals.append(leftVal)
                left -= 1
            } else {
                returnVals.append(rightVal)
                right += 1
            }
        }
        return returnVals.sorted()
    }
}

---

416ms

class Solution {
    
    func findStartIndex(_ arr: [Int], _ x: Int) -> Int {
        var i = 0
        while i < arr.count && arr[i] <= x {
            i += 1
        }
        
        return i
    }
    
    func findClosestElements(_ arr: [Int], _ k: Int, _ x: Int) -> [Int] {
        
        var closest:[Int] = []
        let startIndex = findStartIndex(arr, x)
        var leftRunner:Int = startIndex - 1
        var rightRunner:Int = startIndex
        
        while closest.count < k && (leftRunner >= 0 || rightRunner < arr.count) {           
             
            if leftRunner < 0 {
                closest.append(arr[rightRunner])
                rightRunner += 1
                continue
            } else if rightRunner >= arr.count {
                closest.insert(arr[leftRunner], at: 0)
                leftRunner -= 1
                continue
            }
            
            let left = arr[leftRunner]
            let right = arr[rightRunner]
            
            if abs(x-left) <= abs(x-right) {
                closest.insert(left, at: 0)
                leftRunner -= 1
            } else {
                closest.append(right)
                rightRunner += 1
            }
        }
        
        return closest
    }
}

---

436ms

class Solution {
    func findClosestElements(_ arr: [Int], _ k: Int, _ x: Int) -> [Int] {
        var res = [Int]()
        if x <= arr.first! {
            return Array(arr[0..<k])
        }
        if x >= arr.last! {
            return Array(arr[(arr.count - k)...])
        }
        let index = binarySearch(arr, x)
        var left = index - 1
        var right = index + 1
        res.append(arr[index])
        while res.count < k {
            if left < 0 {
                while res.count != k {
                    res.append(arr[right])
                    right += 1
                }
                break
            } else if right >= arr.count {
                while res.count != k {
                    res.append(arr[left])
                    left -= 1
                }
                break
            } else {
                if (x - arr[left]) <= (arr[right] - x) {
                    res.append(arr[left])
                    left -= 1
                } else {
                    res.append(arr[right])
                    right += 1
                }
            }
        }
        return res.sorted()
    }
    
    private func binarySearch(_ arr: [Int], _ x: Int) -> Int {
        var left = 0
        var right = arr.count - 1
        while left < right {
            let mid = left + (right - left)/2
            if arr[mid] == x {
                return mid
            } else if arr[mid] > x {
                right = mid - 1
            } else {
                left = mid + 1
            }
        }
        return left
    }
}