您好我正在尝试为我的代码找出大0表示法但是遇到了麻烦。我是算法的新手，不知道什么过程增加0（n）到0（n 2 ）。
package gmit;
import java.util.*;
import java.io.*;
import java.nio.charset.Charset;
public class TestRunner {
// Creating Hashmap
private static HashMap<String, String> stringmap = new HashMap<String, String>();
// Creating String Array lists
private static ArrayList<ArrayList<String>> mylist = new ArrayList<ArrayList<String>>();
private static ArrayList<String> lol = new ArrayList<String>();
// Declaring int variables
private static int encryptioncounter=0,decryptioncounter=0,lastindexcounter=0,
mylistindexcounter=0,resortcounter=0;
// Declaring String variables
private static String password,value;
private static String result,text;
// ----------------------------------------------- Main start --------------------------------------------------------
public static void main(String[] args) throws IOException {
System.out.println("Pleaseinput your passphrase");
// Gets user Input
Scanner in = new Scanner(System.in);
password = in.nextLine();
System.out.println("Please input the file name you want to encrypt.(WarAndPeace-LeoTolstoy.txt)");
// Gets user Input
Scanner tin = new Scanner(System.in);
text = tin.nextLine();
//Starts Timer
long startTime = System.nanoTime();
// Method to populate HashMap
putstuffinstrinmap();
// Starts for loop
// Creates Array list in number of the amount of characters of the password
// Adds created arraylists to Arraylist<List> mylist.
for (int i = 0; i < password.length(); i++) {
List<String> firstCharandMore= new ArrayList<>();
char c = password.charAt(i);
firstCharandMore.add(String.valueOf(c));
String resortcountertostring= String.valueOf(resortcounter);
mylist.add((ArrayList<String>) firstCharandMore);
// Adds index for resort to arraylists
mylist.get(i).add(resortcountertostring);
//mylist.add((ArrayList<String>) resortcountertostring);
resortcounter++;
}
// Reads in File in UTF-8 format
// gets back a character
BufferedReader reader = new BufferedReader(
new InputStreamReader(
new FileInputStream(text),
Charset.forName("UTF-8")));
int c;
while((c = reader.read()) != -1) {
char string = (char) c;
// Converts Character to upper case String
// Passes the string into encryption method
encrypt(Character.toString(string).toUpperCase());
// Adds one to counter
decryptioncounter++;
}
//long endTime2 = System.nanoTime();
//long totalTime2 = endTime2 - startTime;
//double seconds2 = (double)totalTime2 / 1000000000.0;
//System.out.println(seconds2+" Encryption");
// Creates new Arraylist listToSort (Copy of mylist)
// Sorts Array lists in alphabetic order by first character from each list
sortarraylists();
writetofileencrypted();
// Resorts arraylists using the index
resortarraylist();
// Calls decryption method
decrypt();
// Calls write to file method
writetofilefin();
// Ends Timer
long endTime = System.nanoTime();
long totalTime = endTime - startTime;
// Prints Time
double seconds = (double)totalTime / 1000000000.0;
System.out.println(seconds+" Total time");
}
// ------------------------------------ End Main -----------------------------------------
// Writes encrypted message to file.
private static void writetofileencrypted() throws FileNotFoundException, UnsupportedEncodingException {
// TODO Auto-generated method stub
PrintWriter writer2 = new PrintWriter("encrypted.txt", "UTF-8");
StringBuilder builder2 = new StringBuilder();
for (ArrayList<String> value : mylist) {
builder2.append(value);
}
String s = builder2.toString();
//String s = lol.toString();
writer2.println(s);
writer2.close();
}
// -------------------------------------resorting-----------------------------------------
private static void resortarraylist() {
// Resorts lists using index 1 (The numbers assigned to that index))
mylist.sort((l1, l2) -> l1.get(1).compareTo(l2.get(1)));
}
// ------------------------------------End resorting --------------------------------------
// ------------------------------------ Sorting ------------------------------------------
private static void sortarraylists() {
// Sorting lists in alphabetical order by index 0
mylist.sort((l1, l2) -> l1.get(0).compareTo(l2.get(0)));
}
// ------------------------------------End sorting ---------------------------------------
// ------------------------------------write to file --------------------------------------
private static void writetofilefin() throws FileNotFoundException, UnsupportedEncodingException {
// Prints to array list lol to file
PrintWriter writer = new PrintWriter("finished.txt", "UTF-8");
StringBuilder builder = new StringBuilder();
for (String value : lol) {
builder.append(value);
}
String s = builder.toString();
//String s = lol.toString();
writer.println(s);
writer.close();
}
// -------------------------------- Encryption Start -------------------------------------
private static void encrypt(String string) {
// Gets coherent value from map
value= stringmap.get(string);
// adds value to mylist at index encryptioncounter
mylist.get(encryptioncounter).add(value);
// Adds one to counter
encryptioncounter++;
// Resets encryptioncounter
if(encryptioncounter>=password.length()){
encryptioncounter=0;
// Adds one to lastindexcounter
lastindexcounter++;
}
}
// --------------------------------- Encryption End ---------------------------------------
// --------------------------------- Decryption Start -------------------------------------
private static void decrypt() {
int thiscounter=0;
// runs until decryptioncounter is = to thiscounter or
// mylistindexcounter is = to lastindexcounter
while(decryptioncounter != thiscounter ){
for(int i=0;i <password.length() ;i++){
// gets value from Arraylist
String ba = mylist.get(i).get(mylistindexcounter);//0(1)
// gets coherent value from map
result= stringmap.get(ba);// 0(n)
// adds value to arraylist lol
lol.add(result);
thiscounter++;
if(mylistindexcounter >=lastindexcounter){
decryptioncounter =thiscounter;
}
}
mylistindexcounter++;
}
}
// ---------------------------------- Decryption End ---------------------------------------
// --------------------------------- Map population start ---------------------------------
// 0(1)
public static void putstuffinstrinmap(){
stringmap.put("AA", "P");//AA - P
stringmap.put("AD", "H");//AD - H
stringmap.put("AF", "0");//
stringmap.put("AG", "Q");//
stringmap.put("AV", "G");//
stringmap.put("AX", "6");//
stringmap.put("DA", "4");//
stringmap.put("DD", "M");//
stringmap.put("DF", "E");//
stringmap.put("DG", "A");//
stringmap.put("DV", "1");//
stringmap.put("DX", "Y");//
stringmap.put("FA", "L");//
stringmap.put("FD", "2");//
stringmap.put("FF", "N");//
stringmap.put("FG", "O");//
stringmap.put("FV", "F");//
stringmap.put("FX", "D");//
stringmap.put("GA", "X");//
stringmap.put("GD", "K");//
stringmap.put("GF", "R");//
stringmap.put("GG", "3");//
stringmap.put("GV", "C");//
stringmap.put("GX", "V");//
stringmap.put("VA", "S");//
stringmap.put("VD", "5");//
stringmap.put("VF", "Z");//
stringmap.put("VG", "W");//
stringmap.put("VV", "7");//
stringmap.put("VX", "B");//
stringmap.put("XA", "J");//
stringmap.put("XD", "9");//
stringmap.put("XF", "U");//
stringmap.put("XG", "T");//
stringmap.put("XV", "I");//
stringmap.put("XX", "8");//
stringmap.put("P", "AA");//
stringmap.put("H", "AD");//
stringmap.put("0", "AF");//
stringmap.put("Q", "AG");//
stringmap.put("G", "AV");//
stringmap.put("6", "AX");//
stringmap.put("4", "DA");//
stringmap.put("M", "DD");//
stringmap.put("E", "DF");//
stringmap.put("A", "DG");//
stringmap.put("1", "DV");//
stringmap.put("Y", "DX");//
stringmap.put("L", "FA");//
stringmap.put("2", "FD");//
stringmap.put("N", "FF");//
stringmap.put("O", "FG");//
stringmap.put("F", "FV");//
stringmap.put("D", "FX");//
stringmap.put("X", "GA");//
stringmap.put("K", "GD");//
stringmap.put("R", "GF");//
stringmap.put("3", "GG");//
stringmap.put("C", "GV");//
stringmap.put("V", "GX");//
stringmap.put("S", "VA");//
stringmap.put("5", "VD");//
stringmap.put("Z", "VF");//
stringmap.put("W", "VG");//
stringmap.put("7", "VV");//
stringmap.put("B", "VX");//
stringmap.put("J", "XA");//
stringmap.put("9", "XD");//
stringmap.put("U", "XF");//
stringmap.put("T", "XG");//
stringmap.put("I", "XV");//
stringmap.put("8", "XX");//
stringmap.put("AH", ".");//
stringmap.put("DH", "!");//
stringmap.put("FH", "?");//
stringmap.put("GH", " ");//
stringmap.put("VH", "'");//
stringmap.put("XH", ",");//
stringmap.put(".", "AH");//
stringmap.put("!", "DH");//
stringmap.put("?", "FH");//
stringmap.put(" ", "GH");//
stringmap.put("'", "VH");//
stringmap.put(",", "XH");//
stringmap.put("AP", "]");//
stringmap.put("DP", "[");//
stringmap.put("FP", "~");//
stringmap.put("GP", "&");//
stringmap.put("VP", ":");//
stringmap.put("XP", ";");//
stringmap.put("AP", "-");//"
stringmap.put("DP", "");//
stringmap.put("FP", "*");//
stringmap.put("GP", "^");//
stringmap.put("VP", "\"");//
stringmap.put(null, " ");//
}
// --------------------------------- Map population End -----------------------------------
}
使用我的代码解释它或指导我阅读一些阅读材料的任何帮助将不胜感激。
答案 0 :(得分：0)
首先，您不需要Total time来查找Big O. Big O表示法用于查找算法中的基本操作计数。就像写n一样，数组的元素是O（n），因为你需要编写每个元素。对于大小为n*n的矩阵，它是O（n ^ 2）。我想，所以我的算法Big O是O（n m + k）。其中n是步数while(decryption counter!= thecounter)循环次数，m是密码长度，k是其他操作，循环。通常k不会添加到Big O，因为它比n m小得多，但在你的情况下我不确定它。