63 lines
2.3 KiB
Swift
63 lines
2.3 KiB
Swift
/**
|
|
* File: binary_search.swift
|
|
* Created Time: 2023-01-28
|
|
* Author: nuomi1 (nuomi1@qq.com)
|
|
*/
|
|
|
|
/* Binary search (double closed interval) */
|
|
func binarySearch(nums: [Int], target: Int) -> Int {
|
|
// Initialize double closed interval [0, n-1], i.e., i, j point to the first element and last element of the array respectively
|
|
var i = nums.startIndex
|
|
var j = nums.endIndex - 1
|
|
// Loop until the search interval is empty (when i > j, it is empty)
|
|
while i <= j {
|
|
let m = i + (j - i) / 2 // Calculate midpoint index m
|
|
if nums[m] < target { // This situation indicates that target is in the interval [m+1, j]
|
|
i = m + 1
|
|
} else if nums[m] > target { // This situation indicates that target is in the interval [i, m-1]
|
|
j = m - 1
|
|
} else { // Found the target element, thus return its index
|
|
return m
|
|
}
|
|
}
|
|
// Did not find the target element, thus return -1
|
|
return -1
|
|
}
|
|
|
|
/* Binary search (left closed right open interval) */
|
|
func binarySearchLCRO(nums: [Int], target: Int) -> Int {
|
|
// Initialize left closed right open interval [0, n), i.e., i, j point to the first element and the last element +1 of the array respectively
|
|
var i = nums.startIndex
|
|
var j = nums.endIndex
|
|
// Loop until the search interval is empty (when i = j, it is empty)
|
|
while i < j {
|
|
let m = i + (j - i) / 2 // Calculate midpoint index m
|
|
if nums[m] < target { // This situation indicates that target is in the interval [m+1, j)
|
|
i = m + 1
|
|
} else if nums[m] > target { // This situation indicates that target is in the interval [i, m)
|
|
j = m
|
|
} else { // Found the target element, thus return its index
|
|
return m
|
|
}
|
|
}
|
|
// Did not find the target element, thus return -1
|
|
return -1
|
|
}
|
|
|
|
@main
|
|
enum BinarySearch {
|
|
/* Driver Code */
|
|
static func main() {
|
|
let target = 6
|
|
let nums = [1, 3, 6, 8, 12, 15, 23, 26, 31, 35]
|
|
|
|
/* Binary search (double closed interval) */
|
|
var index = binarySearch(nums: nums, target: target)
|
|
print("Index of target element 6 = \(index)")
|
|
|
|
/* Binary search (left closed right open interval) */
|
|
index = binarySearchLCRO(nums: nums, target: target)
|
|
print("Index of target element 6 = \(index)")
|
|
}
|
|
}
|