我正在尝试修改此堆算法,该算法显示字符串输入的所有可能排列。我正在尝试修改代码,以便能够与带有编写器文件的Scanner类一起使用。当我尝试写入新文件时,它没有按原样添加所有24个字符串,而是添加了前4个字符串。由于它是void方法,因此无法使用pw.println(obj.heapPermutation(a,a。长度,a.length))。有解决此问题的建议吗?
谢谢
P.S。我在网上找到了此代码,并且我承认这不是我的。
import java.util.Scanner;
import java.io.*;
import static java.lang.System.*;
class HeapAlgo
{
void heapPermutation(String a[], int size, int n) throws IOException
{
FileWriter fw = new FileWriter("note.txt");
PrintWriter pw = new PrintWriter(fw);
// if size becomes 1 then prints the obtained
// permutation
if (size == 1)
for (int i=0; i<n; i++)
{
System.out.println(a[i] + "");
}
for (int i=0; i<size; i++)
{
heapPermutation(a, size-1, n);
// if size is odd, swap first and last
// element
if (size % 2 == 1)
{
String temp = a[0];
a[0] = a[size-1];
a[size-1] = temp;
}
// If size is even, swap ith and last
// element
else
{
String temp = a[i];
a[i] = a[size-1];
a[size-1] = temp;
}
}
}
public static void main(String args[]) throws IOException
{
HeapAlgo obj = new HeapAlgo();
String a[] = new String["abcd","bbbb","cccc","dddd"];
obj.heapPermutation(a, a.length, a.length);
答案 0 :(得分:1)
您的PrintWriter
在heapPermutation方法中初始化,因为它被递归调用,heapPermutation(a, size-1, n)
每次都会被覆盖。我相信此操作的默认行为是替换文件,而不是附加文件。
您应该创建一个构造函数来初始化PrintWriter
,以便不会每次都重新初始化。
class HeapAlgo {
// create a writer at the class level
private PrintWriter _pw;
// Create a constructor to assign the writer
public HeapAlgo(PrintWriter pw) {
this._pw = pw;
}
void heapPermutation(String a[], int size, int n) throws IOException {
// if size becomes 1 then prints the obtained
// permutation
if (size == 1)
for (int i=0; i<n; i++) {
System.out.println(a[i] + "");
this._pw.print(a[i] + ""); // print here I belive?
}
for (int i=0; i<size; i++) {
heapPermutation(a, size-1, n);
// if size is odd, swap first and last
// element
if (size % 2 == 1) {
String temp = a[0];
a[0] = a[size-1];
a[size-1] = temp;
}
// If size is even, swap ith and last
// element
else {
String temp = a[i];
a[i] = a[size-1];
a[size-1] = temp;
}
}
}
}
public static void main(String args[]) throws IOException {
FileWriter fw = new FileWriter("note.txt");
PrintWriter pw = new PrintWriter(fw);
HeapAlgo obj = new HeapAlgo(pw); // Pass in a writer
String a[] = new String["abcd","bbbb","cccc","dddd"];
obj.heapPermutation(a, a.length, a.length);