ทำยังไงให้เข้าใจโครงสร้างข้อมูลอัลกอริทึ่มมากขึ้นคะ (java) เราพยายามแล้วค่ะซื้อหนังสือมาอ่าน อ่านตามห้องสมุด หาตามเนต ใช้stackoverflow
แล้วยังไม่รู้เรื่องค่ะ ไม่รู้ว่าเป็นเพราะสมองเราlogicต่ำหรือเปล่าไม่รู้ ทฤษฏีอาจจะถูไปได้(แต่ก็สอบตกเหลืออีก3คะแนนจะผ่าน) พอมาแปลงเป็นโค้ดจาวาเรางงมากเลยค่ะ ใครมีเทคนิคดีๆได้โปรดช่วยชี้แนะทีค่ะ พลีสสสสส ขอบคุณค่ะ

[Spoil] คลิกเพื่อดูข้อความที่ซ่อนไว้เรารู้สึกแย่มากคือเท่าไหร่ก็ไม่เข้าใจ ไปต่อไม่ได้ โดนทิ้งไว้กลางทาง

นี่โค้ดเราค่ะ เราพยายามแล้ว แต่กดช้อยต์สามมันไม่ออก....อะไรเลยค่ะ
import java.util.Scanner;
class ArithmeticExpression
{
    public static void main(String args[])
    {
        Scanner kb = new Scanner(System.in);
      IntArrayStack stack = new IntArrayStack();
        int choice=0,index;
      String output, expression = "";
      char ch,ch1,ch2;
      int o=0,v=0,answer=0;
      int result;
        
        do{
        System.out.println("=============Menu==========");
        System.out.println("= 1. Input Infix          =");
        System.out.println("= 2. Convert to Postfix   =");
        System.out.println("= 3. Calculate Expression =");
        System.out.println("= 0. Exit                =");
        System.out.println("=============Menu==========");
        System.out.print("===>Select choice ::");
        choice=kb.nextInt();
        switch(choice)
        {
                case 1:    System.out.print("Input Infixed Expression : ");
                     expression = kb.next();
                     break;
                case 2:    output = "";
                     for(int i = 0;i <expression.length();i++)
                     {
                        ch = expression.charAt(i);
                        if ((ch >= 'A' && ch <= 'Z')||(ch >= 'a' && ch <= 'z'))
                        {
                           output = output + ch;
                        }
                        else if (stack.isEmpty())
                        {
                           stack.push(ch);
                        }
                        else if (ch =='(')
                        {
                           stack.push(ch);
                        }
                        else if (ch == ')')
                        {
                           while(stack .top() != ')')
                              output = output + (char)stack.pop();
                           stack.pop();
                        }
                        else
                        {
                           if (priority(ch) > priority((char)stack.top()))
                           {
                              stack.push(ch);
                           }
                           else
                           {
                              while(priority(ch) <= priority((char)stack.top()))
                                 output = output + (char)stack.pop();
                              stack.push(ch);
                           }
                        }
                     }
                     while(!stack.isEmpty())
                     {
                        output = output + (char)stack.pop();
                     }
                     System.out.println("Porfixed Expression is "+output);
                     break;
                case 3:    //a to i 1 --> 9
                     output = "";
                     int a,A = 1;
                     int b,B = 2;
                     int c,C = 3;
                     int d,D = 4;
                     int e,E = 5;
                     int f,F = 6;
                     int g,G = 7;
                     int h,H = 8;
                     int i,I = 9;
                     for(int w = 0;w <expression.length();w++)
                     {
                        ch = expression.charAt(w);
                        if((ch=='+')||(ch=='-')||(ch=='*')||(ch=='/'))
                        {
                           ch1=(char)stack.pop();
                           ch2=(char)stack.pop();
                           if(ch1 == 'A') o = A;   
                           else if(ch1 == 'B') o = B;
                           else if(ch1 == 'C') o = C;
                           else if(ch1 == 'D') o = D;
                           else if(ch1 == 'E') o = E;
                           else if(ch1 == 'F') o = F;
                           else if(ch1 == 'G') o = G;
                           else if(ch1 == 'H') o = H;
                           else if(ch1 == 'I') o = I;
                           if(ch2 == 'A') v = A;
                           else if(ch2 == 'B') v = B;
                           else if(ch2 == 'C') v = C;
                           else if(ch2 == 'D') v = D;
                           else if(ch2 == 'E') v = E;
                           else if(ch2 == 'F') v = F;
                           else if(ch2 == 'G') v = G;
                           else if(ch2 == 'H') v = H;
                           else if(ch2 == 'I') v = I;
                           
                           if(ch== '+') answer = o+v;
                           else if(ch== '-') answer = o-v;
                           else if(ch== '*') answer = o*v;
                           else if(ch== '/') answer = o/v;
                           stack.push(answer);
                        }
                        else if (stack.isEmpty())
                        {
                           stack.push(ch);
                        }
                        else if (ch =='(')
                        {
                           stack.push(ch);
                        }
                        else if (ch == ')')
                        {
                           while(stack .top() != ')')
                              output = output + (char)stack.pop();
                           stack.pop();
                        }
                        else
                        {
                           if (priority(ch) > priority((char)stack.top()))
                           {
                              stack.push(ch);
                           }
                           else
                           {
                              while(priority(ch) <= priority((char)stack.top()))
                                 output = output + (char)stack.pop();
                              stack.push(ch);
                           }
                        }

                     }
                     while(!stack.isEmpty())
                     {
                        output = output + (char)stack.pop();
                     }
                     System.out.println("Postfix Calculate is "+answer);
                     break;
                case 0:    System.exit(0);
                default: System.out.println("Invalid choice");
            }
        }while(choice!=0);
    }


    public static int priority(char ch)
    {
      if(ch=='^')
         return 3;
        if(ch=='+' || ch=='-')
            return 1;
        if(ch=='*' || ch=='/')
            return 2;
        return 0;
    }
}