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49 lines
1.1 KiB
49 lines
1.1 KiB
/**
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* File: binary_search_recur.kt
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* Created Time: 2024-01-25
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* Author: curtishd (1023632660@qq.com)
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*/
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package chapter_divide_and_conquer.binary_search_recur
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/* 二分查找：问题 f(i, j) */
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fun dfs(
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nums: IntArray,
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target: Int,
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i: Int,
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j: Int
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): 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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val m = (i + j) / 2
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return if (nums[m] < target) {
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// 递归子问题 f(m+1, j)
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dfs(nums, target, m + 1, 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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dfs(nums, target, i, 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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m
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}
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}
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/* 二分查找 */
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fun binarySearch(nums: IntArray, target: Int): Int {
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val n = nums.size
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// 求解问题 f(0, n-1)
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return dfs(nums, target, 0, n - 1)
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}
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/* Driver Code */
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fun main() {
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val target = 6
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val nums = intArrayOf(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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val index = binarySearch(nums, target)
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println("目标元素 6 的索引 = $index")
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} |