[英]OutOfMemoryError on BigInteger
我正在為BigIntegers編寫一個波蘭表示法計算器(只是*,^和!),我在行中得到一個OutOfMemoryError
,我正在減去BigInteger.ONE
以使factorial工作,為什么?
package polish_calculator;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.util.Stack;
public class Main {
static BigInteger factorial(BigInteger number){
Stack <BigInteger> factorialStack = new Stack<BigInteger>();
factorialStack.push(number);
while (!number.equals(BigInteger.ONE)){ //load the stack
factorialStack.push(number.subtract(BigInteger.ONE)); // here's the error
}
BigInteger result = BigInteger.ONE;
while(!factorialStack.empty()){ // empty and multiply the stack
result.multiply(factorialStack.pop());
}
return result;
}
public static void main(String[] args) throws IOException {
BigInteger testFactorial = new BigInteger("12");
System.out.println(factorial(testFactorial));
Stack <String> stack = new Stack<String>();
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String readExpression = br.readLine();
while(!readExpression.equals("")){
String [] splittedExpression = readExpression.split(" ");
for(int i=0; i<splittedExpression.length;i++){
if(splittedExpression[i].equals("*"))
{
BigInteger operand1 = new BigInteger(stack.pop());
BigInteger operand2 = new BigInteger(stack.pop());
BigInteger result = operand1.multiply(operand2);
String stackString = result.toString();
stack.push(stackString);
}
if(splittedExpression[i].equals("^"))
{
BigInteger operand1 = new BigInteger(stack.pop());
BigInteger operand2 = new BigInteger(stack.pop());
BigInteger result = operand1.modPow(operand2, BigInteger.ONE);
String stackString = result.toString();
stack.push(stackString);
}
if(splittedExpression[i].equals("!"))
{
BigInteger operand1 = new BigInteger(stack.pop());
BigInteger result = factorial(operand1);
String stackString = result.toString();
stack.push(stackString);
}
else{ //it's an integer
stack.push(splittedExpression[i]);
}
} // end for splittedExpression.length
}
}
}
錯誤:
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.math.BigInteger.subtract(BigInteger.java:1118)
at polish_calculator.Main.factorial(Main.java:45)
at polish_calculator.Main.main(Main.java:65)
Java Result: 1
BigInteger.subtract生成一個新的BigInteger,您將其推入堆棧。
但原始數字仍然相同,所以條件!number.equals(BigInteger.ONE)永遠不會成立。
因此,您將使用數字1的副本永久填充堆棧,直到內存不足為止
編輯(再次):
注意,這也是一種非常需要內存的計算階乘的方法,因為你需要在棧上推N個來計算N! 隨着時間的推移將它們相乘可能會更好,盡管在因子變得非常大之前你當然不需要大的N.
有關有效計算大因子的一些詳細信息,請參見http://en.wikipedia.org/wiki/Factorial 。
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