[Swift]二分法的两种方式

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➤微信公众号：山青咏芝（shanqingyongzhi）
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扩展数组:

extension Array
{    
    //二分法方式1
    func binarySearch(_ nums:[Int],_ target: Int) -> Int
    {
        var low = 0
        var high = nums.count - 1
        var mid = (low + high) >> 1
        
        while low <= high {
            let val = nums[mid]
            if target == val {
                return mid
            } else if target < val {
                high = mid - 1
            } else {
                low = mid + 1 
            }
            mid = (low + high) >> 1
        }
        return high
    }
    
    //二分法方式2
    func binarySearch(_ nums:[Int],_ start: Int, _ end: Int,_ target: Int) -> Int
    {
        let mid = start + (end - start) / 2
        if nums[mid] >= target && (start == mid || nums[mid - 1] < target) 
        { 
            return mid 
        }
        if nums[mid] < target 
        {
            return binarySearch(nums,target, mid + 1, end)
        }
        return binarySearch(nums,target, start, mid - 1)
    }
}

测试代码：

//注：不含有元素5
var arr = [1,2,3,4,6,7,8,9]
print(arr.binarySearch(arr,5))
//Print 3
print(arr.binarySearch(arr,0,arr.count,5))
//Print 4

//注：含有元素6
print(arr.binarySearch(arr,6))
//Print 4
print(arr.binarySearch(arr,0,arr.count,6))
//Print 4