46 lines
1.2 KiB
Swift
46 lines
1.2 KiB
Swift
/**
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* File: binary_search_recur.swift
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* Created Time: 2023-09-02
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* Author: nuomi1 (nuomi1@qq.com)
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*/
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/* 二分查找：问题 f(i, j) */
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func dfs(nums: [Int], target: Int, i: Int, j: Int) -> Int {
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// 若区间为空，代表无目标元素，则返回 -1
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if i > j {
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return -1
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}
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// 计算中点索引 m
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let m = (i + j) / 2
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if nums[m] < target {
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// 递归子问题 f(m+1, j)
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return dfs(nums: nums, target: target, i: m + 1, j: j)
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} else if nums[m] > target {
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// 递归子问题 f(i, m-1)
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return dfs(nums: nums, target: target, i: i, j: m - 1)
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} else {
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// 找到目标元素，返回其索引
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return m
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}
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}
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/* 二分查找 */
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func binarySearch(nums: [Int], target: Int) -> Int {
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let n = nums.count
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// 求解问题 f(0, n-1)
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return dfs(nums: nums, target: target, i: 0, j: n - 1)
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}
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@main
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enum BinarySearchRecur {
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/* Driver Code */
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static func main() {
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let target = 6
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let nums = [1, 3, 6, 8, 12, 15, 23, 26, 31, 35]
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// 二分查找（双闭区间）
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let index = binarySearch(nums: nums, target: target)
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print("目标元素 6 的索引 = \(index)")
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}
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}
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