442 - Matrix Chain Multiplication

http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=383

//type:stack
import java.util.*;

public class Main {
 
 public static void main(String[] args) {
  Scanner scan = new Scanner(System.in);
  Matrix[] matrix = new Matrix[26];
  int num = scan.nextInt();
  int index=0;
  while(num--!=0){ //The first part
   char name = (scan.next()).toCharArray()[0];
   int row = scan.nextInt();
   int column = scan.nextInt();
   scan.nextLine();
 
   matrix[(int)(name)-65]=new Matrix(name,row,column);/*-65的用意；把字母從0開始排列，
   大A的Ascii碼從65開始，配合26字母Matrix擺放*/
  } 
  A:
  while(scan.hasNext()){//The second part
   int total=0;
   Stack<Matrix> m = new Stack<Matrix>();
   String exp = scan.nextLine();
   for(int i=0 ; i<exp.length() ; i++){
    
    if(exp.charAt(i)=='('){
     
    }
     
    else if(exp.charAt(i)==')'){
     Matrix rightM = m.pop(); //先進後出，stack的特性
     Matrix leftM = m.pop();
     if(leftM.column!=rightM.row){
      System.out.println("error");
      continue A;
     }
     else{
      total+=leftM.row*leftM.column*rightM.column;
      m.push(new Matrix('t',leftM.row,rightM.column));
     }
    }
    
    else//沒有以上狀況就是matrix，放入stack裡
     m.push(matrix[(int)exp.charAt(i)-65]);    
   }   
  
   //到了最右邊的)跳出後，會有三種情況，一個是stack裡面剩一個matrix;剩兩個;剩三個以上
   if(m.size()>2){
    System.out.println("error");
    continue A;
   }
   else if(m.size()==2){
    Matrix rightM = m.pop();
    Matrix leftM = m.pop();
    if(leftM.column!=rightM.row){
     System.out.println("error");
     continue A;
    }
    else
     total+=leftM.row*leftM.column*rightM.column;   
   }
   System.out.println(total);
 }
 
}
}
class Matrix{
 public char matrix;
 public int row,column;
 public Matrix(char matrix,int row,int column){
  this.matrix=matrix;
  this.row=row;
  this.column=column;
 }
}