如何原地反转数组(不创建新数组)?
public static int[] reverseArrayWithoutTempArray(int[] array) {
int i = 0, j = array.length - 1;
for (i = 0; i < array.length / 2; i++, j--) {
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
return array;
}
我的作业只要求伪代码,你没有明确指定想要用什么编程语言,这使得任务相对简单 :-)
请用你自己喜欢的编程语言实现:
Set i1 to index of first element in array
Set i2 to index of last element in array
while i1 < i2:
Set temporary variable to element number i1
Set element number i1 to element number i2
Set element number i2 to temporary value
Add 1 to i1
Subtract 1 from i2
一个理想的做法是在脑海中运行该算法,并使用一张纸来跟踪变量:
i1
和 i2
。临时变量
。对于较简单的算法,我倾向于这样做。对于更难的算法,我会插入调试语句,让计算机为我完成这些困难的工作。从一张纸开始:
i1 | i2 | tempvar | el[0] | el[1] | el[2] | el[3] | el[4] | el[5]
---+----+---------+-------+-------+-------+-------+-------+------
H e l l o !
只需按照每个步骤逐一进行,检查和/或更改每个列项。这将使您比仅仅获得一些代码更好地理解其工作原理。
import java.util.*;
//Reverse string array
public static void reverseArray(String[] array){
int middle = array.length / 2;
String temp;
int j = array.length -1;
for (int i = 0 ; i < middle; i++) {
temp = array[i];
array[i] = array[j];
array[j] = temp;
j--;
}
System.out.println(Arrays.toString(array));
}
public static void reverseArray(String[] array)
改为 public static void reverseArray(int[] array)
,并且将 String temp
改为 int temp
。public static void main (String[] args) throws java.lang.Exception{
String[] array = {"Smith", "Peter", "Michel", "John"};
reverseArray(array);
}
输出:
[John, Michel, Peter, Smith]
不创建新数组反转字符数组
public static void main(String[] args) {
char[] a = {'1', '2', '3','4'};
char temp = ' ';
for (int i = 0; i < a.length / 2; i++) {
temp = a[i];
a[i] = a[a.length - 1 - i];
a[a.length - 1 - i] = temp;
}
System.out.println(a);
}
temp = a[0]
a[0] = a[size - 1]
a[size - 1] = temp
等等。
size - 1
,而不是 size - 2
。 - Thomasfor (int start = 0, end = length-1; start < end; ++start,--end) swap(array,start,end);
中检查那个条件,循环怎么会终止呢? - Pete Kirkhampublic static void main(String args[]){
int j=arr.length;
for(int i=0;i<arr.length/2;i++){
int temp=arr[i];
arr[i]=arr[j-1-i];
arr[j-1-i]=temp;}
for(int i=0;i<arr.length;i++){
System.out.println(arr[i]);
}
}
这里是一个不使用临时变量或另一个数组来反转数组元素的解决方案。这仅适用于Java 8及以上版本。
void invertUsingStreams(Object[] arr2) {
IntStream.rangeClosed(1,arr2.length)
.mapToObj(i -> arr2[arr2.length-i])
.forEach(System.out::println);
}
谢谢,
这里有一个完整的程序,只需复制粘贴并在您的IDE中运行:
public class ReverseArrayWithoutAnotherArray {
public static void main(String[] args) {
int[] array = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int middle = array.length / 2;
int temp;
int j = array.length -1;
for(int a : array){
System.out.println(" before reverse :: " + a);
}
for (int i = 0 ; i < middle; i++, j--) {
temp = array[i];
array[i] = array[j];
array[j] = temp;
}
for(int a : array){
System.out.println(" after reverse :: " + a);
}
}
}
输出:
before reverse :: 1
before reverse :: 2
before reverse :: 3
before reverse :: 4
before reverse :: 5
before reverse :: 6
before reverse :: 7
before reverse :: 8
before reverse :: 9
before reverse :: 10
after reverse :: 10
after reverse :: 9
after reverse :: 8
after reverse :: 7
after reverse :: 6
after reverse :: 5
after reverse :: 4
after reverse :: 3
after reverse :: 2
after reverse :: 1
Array.prototype.reverse = function() {
for(var i = 0, j = this.length-1; i < j; i++, j--) {
var tmp = this[i];
this[i] = this[j];
this[j] = tmp;
}
return this;
};