mirror of
https://github.com/krahets/hello-algo.git
synced 2024-12-27 00:06:28 +08:00
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
58 lines
2.1 KiB
Java
58 lines
2.1 KiB
Java
/**
|
|
* File: binary_search.java
|
|
* Created Time: 2022-11-25
|
|
* Author: Krahets (krahets@163.com)
|
|
*/
|
|
|
|
package chapter_searching;
|
|
|
|
public class binary_search {
|
|
/* 二分查找（双闭区间） */
|
|
static int binarySearch(int[] nums, int target) {
|
|
// 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
|
|
int i = 0, j = nums.length - 1;
|
|
// 循环，当搜索区间为空时跳出（当 i > j 时为空）
|
|
while (i <= j) {
|
|
int m = i + (j - i) / 2; // 计算中点索引 m
|
|
if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j] 中
|
|
i = m + 1;
|
|
else if (nums[m] > target) // 此情况说明 target 在区间 [i, m-1] 中
|
|
j = m - 1;
|
|
else // 找到目标元素，返回其索引
|
|
return m;
|
|
}
|
|
// 未找到目标元素，返回 -1
|
|
return -1;
|
|
}
|
|
|
|
/* 二分查找（左闭右开区间） */
|
|
static int binarySearchLCRO(int[] nums, int target) {
|
|
// 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
|
|
int i = 0, j = nums.length;
|
|
// 循环，当搜索区间为空时跳出（当 i = j 时为空）
|
|
while (i < j) {
|
|
int m = i + (j - i) / 2; // 计算中点索引 m
|
|
if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j) 中
|
|
i = m + 1;
|
|
else if (nums[m] > target) // 此情况说明 target 在区间 [i, m) 中
|
|
j = m;
|
|
else // 找到目标元素，返回其索引
|
|
return m;
|
|
}
|
|
// 未找到目标元素，返回 -1
|
|
return -1;
|
|
}
|
|
|
|
public static void main(String[] args) {
|
|
int target = 6;
|
|
int[] nums = { 1, 3, 6, 8, 12, 15, 23, 26, 31, 35 };
|
|
|
|
/* 二分查找（双闭区间） */
|
|
int index = binarySearch(nums, target);
|
|
System.out.println("目标元素 6 的索引 = " + index);
|
|
|
|
/* 二分查找（左闭右开区间） */
|
|
index = binarySearchLCRO(nums, target);
|
|
System.out.println("目标元素 6 的索引 = " + index);
|
|
}
|
|
}
|