我正在嘗試修改此堆算法，以顯示字符串輸入的所有可能排列。我正在嘗試修改代碼，以便能夠與帶有編寫器文件的 Scanner 類一起使用。當(dāng)我嘗試寫入一個(gè)新文件時(shí)，它不會(huì)添加所有 24 個(gè)字符串，而是添加前 4 個(gè)。因?yàn)樗且粋€(gè) void 方法，我不能使用 pw.println(obj.heapPermutation(a, a.長(zhǎng)度，a.長(zhǎng)度））。有什么建議可以解決這個(gè)問題嗎？謝謝PS我在網(wǎng)上找到了這段代碼，我承認(rèn)它不是我的。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);
1 回答
慕標(biāo)琳琳
TA貢獻(xiàn)1830條經(jīng)驗(yàn) 獲得超9個(gè)贊
你PrintWriter在 heapPermutation 方法中被初始化，因?yàn)樗沁f歸調(diào)用的，heapPermutation(a, size-1, n)每次都會(huì)被覆蓋。我相信默認(rèn)行為是替換文件，而不是附加到它。
您應(yīng)該創(chuàng)建一個(gè)構(gòu)造函數(shù)來初始化它，PrintWriter因此它不會(huì)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);
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