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46 lines
1.3 KiB
46 lines
1.3 KiB
/**
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* File: binary_search_recur.java
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* Created Time: 2023-07-17
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* Author: krahets (krahets@163.com)
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*/
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package chapter_divide_and_conquer;
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public class binary_search_recur {
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/* 二分查找：问题 f(i, j) */
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static int dfs(int[] nums, int target, int i, int j) {
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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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int 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, 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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return 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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return m;
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}
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}
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/* 二分查找 */
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static int binarySearch(int[] nums, int target) {
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int n = nums.length;
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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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public static void main(String[] args) {
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int target = 6;
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int[] 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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int index = binarySearch(nums, target);
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System.out.println("目标元素 6 的索引 = " + index);
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}
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}
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