mirror of
https://github.com/krahets/hello-algo.git
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e720aa2d24
* Sync recent changes to the revised Word. * Revised the preface chapter * Revised the introduction chapter * Revised the computation complexity chapter * Revised the chapter data structure * Revised the chapter array and linked list * Revised the chapter stack and queue * Revised the chapter hashing * Revised the chapter tree * Revised the chapter heap * Revised the chapter graph * Revised the chapter searching * Reivised the sorting chapter * Revised the divide and conquer chapter * Revised the chapter backtacking * Revised the DP chapter * Revised the greedy chapter * Revised the appendix chapter * Revised the preface chapter doubly * Revised the figures
59 lines
2.2 KiB
C#
59 lines
2.2 KiB
C#
/**
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* File: binary_search.cs
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* Created Time: 2022-12-23
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* Author: haptear (haptear@hotmail.com)
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*/
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namespace hello_algo.chapter_searching;
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public class binary_search {
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/* 二分查找（双闭区间） */
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int BinarySearch(int[] nums, int target) {
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// 初始化双闭区间 [0, n-1] ，即 i, j 分别指向数组首元素、尾元素
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int i = 0, j = nums.Length - 1;
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// 循环，当搜索区间为空时跳出（当 i > j 时为空）
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while (i <= j) {
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int m = i + (j - i) / 2; // 计算中点索引 m
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if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j] 中
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i = m + 1;
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else if (nums[m] > target) // 此情况说明 target 在区间 [i, m-1] 中
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j = m - 1;
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else // 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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// 未找到目标元素，返回 -1
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return -1;
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}
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/* 二分查找（左闭右开区间） */
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int BinarySearchLCRO(int[] nums, int target) {
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// 初始化左闭右开区间 [0, n) ，即 i, j 分别指向数组首元素、尾元素+1
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int i = 0, j = nums.Length;
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// 循环，当搜索区间为空时跳出（当 i = j 时为空）
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while (i < j) {
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int m = i + (j - i) / 2; // 计算中点索引 m
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if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j) 中
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i = m + 1;
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else if (nums[m] > target) // 此情况说明 target 在区间 [i, m) 中
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j = m;
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else // 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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// 未找到目标元素，返回 -1
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return -1;
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}
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[Test]
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public void Test() {
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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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Console.WriteLine("目标元素 6 的索引 = " + index);
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/* 二分查找（左闭右开区间） */
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index = BinarySearchLCRO(nums, target);
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Console.WriteLine("目标元素 6 的索引 = " + index);
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}
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}
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