Java 中的 Arrays.binarySearch()示例| Set 1
原文:https://www . geesforgeks . org/arrays-binary search-Java-examples-set-1/
Arrays.binarySearch() 方法使用二分搜索法算法在给定数据类型的指定数组中搜索指定值。在进行此调用之前，必须按照 Arrays.sort() 方法对数组进行排序。如果没有排序，结果是未定义的。如果数组包含多个具有指定值的元素，则不能保证找到哪一个。让我们浏览下面提供的插图。
图解:
Searching for 35 in byteArr[] = {10,20,15,22,35}
will give result as 4 as it is the index of 35
Searching for g in charArr[] = {'g','p','q','c','i'}
will give result as 0 as it is the index of 'g'
Searching for 22 in intArr[] = {10,20,15,22,35};
will give result as 3 as it is the index of 22
Searching for 1.5 in doubleArr[] = {10.2,15.1,2.2,3.5}
will give result as -1 as it is the insertion point of 1.5
Searching for 35.0 in floatArr[] = {10.2f,15.1f,2.2f,3.5f}
will give result as -5 as it is the insertion point of 35.0
Searching for 5 in shortArr[] = {10,20,15,22,35}
will give result as -1 as it is the insertion point of 5
在 Java 中寻找排序数组中的元素是最简单有效的方法
语法:
public static int binarySearch(data_type arr, data_type key)
记住:这里的数据类型可以是任何原始数据类型，例如字节、字符、双精度、int、float、short、long，甚至 object。
参数:
- Array to be searched
- Value to be searched
返回类型:搜索关键字的索引，如果包含在数组中；否则，(-(插入点)–1)。插入点定义为将键插入数组的点:大于键的第一个元素的索引，如果数组中的所有元素都小于指定的键，则为. length。请注意，这保证了当且仅当找到密钥时，返回值将为> = 0。
有一些重要的点需要记住如下:
- If the input list is not sorted, the result is undefined.
- If there are duplicates, there is no guarantee which one will be found.
如上所述，我们已经讨论过，我们可以通过arrays . binary search()vscollections . binary search()来操作这个算法。 Arrays.binarysearch()适用于也可以是原始数据类型的数组。收藏。binarysearch()适用于对象集合，如数组列表和链接列表。
例 1:
Java
// Java program to demonstrate working of Arrays.
// binarySearch() in a sorted array
// Importing Arrays class from
// java.util package
import java.util.Arrays;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Declaring and initializing byte arrays
// to search over them
byte byteArr[] = { 10, 20, 15, 22, 35 };
char charArr[] = { 'g', 'p', 'q', 'c', 'i' };
int intArr[] = { 10, 20, 15, 22, 35 };
double doubleArr[] = { 10.2, 15.1, 2.2, 3.5 };
float floatArr[] = { 10.2f, 15.1f, 2.2f, 3.5f };
short shortArr[] = { 10, 20, 15, 22, 35 };
// Using sort() method of Arrays class
// and passing arrays to be sorted as in arguments
Arrays.sort(byteArr);
Arrays.sort(charArr);
Arrays.sort(intArr);
Arrays.sort(doubleArr);
Arrays.sort(floatArr);
Arrays.sort(shortArr);
// Primitive datatypes
byte byteKey = 35;
char charKey = 'g';
int intKey = 22;
double doubleKey = 1.5;
float floatKey = 35;
short shortKey = 5;
// Now in sorted array array we will fetch and
// return elements/indiciesaccessing indexes to show
// array is really sorted
// Print commands where we are implementing
System.out.println(
byteKey + " found at index = "
+ Arrays.binarySearch(byteArr, byteKey));
System.out.println(
charKey + " found at index = "
+ Arrays.binarySearch(charArr, charKey));
System.out.println(
intKey + " found at index = "
+ Arrays.binarySearch(intArr, intKey));
System.out.println(
doubleKey + " found at index = "
+ Arrays.binarySearch(doubleArr, doubleKey));
System.out.println(
floatKey + " found at index = "
+ Arrays.binarySearch(floatArr, floatKey));
System.out.println(
shortKey + " found at index = "
+ Arrays.binarySearch(shortArr, shortKey));
}
}
输出
35 found at index = 4
g found at index = 1
22 found at index = 3
1.5 found at index = -1
35.0 found at index = -5
5 found at index = -1
这种方法有多种变体，在这些变体中，我们还可以指定要搜索的数组范围。我们将在以后的文章中讨论这个问题以及在对象数组中进行搜索。
例 2:
Java
// Java Program to Illustrate binarySearch() method
// of Collections class
// Importing required classes
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating empty List
List<Integer> al = new ArrayList<Integer>();
// Adding elements to the List
al.add(12);
al.add(53);
al.add(23);
al.add(46);
al.add(54);
// Using binarySearch() method of Collections class
// over random inserted element and storing the
// index
int index = Collections.binarySearch(al, 23);
// Print and display the indedx
System.out.print(index);
}
}
输出
2
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