[英]Convert a Postfix expression to infix and calculate the postfix and give the answer
我一直在研究該程序,以接收后綴表達式,計算並打印出答案,並將其轉換為中綴表達式。 我已經將計算部分工作了。 例如,如果我輸入2 2 +(說明間距),它將得到4。但是,對於其中的中綴部分,它將輸出2+。 然后,我嘗試了它,沒有任何間距。 我輸入了22+。 后綴不起作用,但是中綴正確打印出來。 因此,我不確定如何修復此部分。 這是我的代碼。
import java.util.NoSuchElementException;
import java.util.Stack;
public class ExpressionTree
{
private final String postfix;
private TreeNode root;
/**
* Takes in a valid postfix expression and later its used to construct the expression tree.
* The posfix expression, if invalid, leads to invalid results
*
* @param postfix the postfix expression.
*/
public ExpressionTree(String postfix)
{
if (postfix == null) { throw new NullPointerException("The posfix should not be null"); }
if (postfix.length() == 0) { throw new IllegalArgumentException("The postfix should not be empty"); }
this.postfix = postfix;
}
private static class TreeNode
{
TreeNode left;
char ch;
TreeNode right;
TreeNode(TreeNode left, char ch, TreeNode right) {
this.left = left;
this.ch = ch;
this.right = right;
}
}
private boolean isOperator(char c) {
return c == '+' || c == '-' || c == '*' || c == '/';
}
/**
* Constructs an expression tree, using the postfix expression
*/
public void createExpressionTree()
{
final Stack<TreeNode> nodes = new Stack<TreeNode>();
for (int i = 0; i < postfix.length(); i++)
{
char ch = postfix.charAt(i);
if (isOperator(ch))
{
TreeNode rightNode = nodes.pop();
TreeNode leftNode = nodes.pop();
nodes.push(new TreeNode(leftNode, ch, rightNode));
} else
{
nodes.add(new TreeNode(null, ch, null));
}
}
root = nodes.pop();
}
/**
* Returns the infix expression
*
* @return the string of infix.
*/
public String infix()
{
if (root == null)
{
throw new NoSuchElementException("The root is empty, the tree has not yet been constructed.");
}
final StringBuilder infix = new StringBuilder();
inOrder(root, infix);
return infix.toString();
}
private void inOrder(TreeNode node, StringBuilder infix) {
if (node != null) {
inOrder(node.left, infix);
infix.append(node.ch);
inOrder(node.right, infix);
}
}
public Double evaluate(String postfix)
{
Stack<Double> s = new Stack<Double>();
char[] chars = postfix.toCharArray();
int N = chars.length;
for(int i = 0; i < N; i++)
{
char ch = chars[i];
if(isOperator(ch))
{
switch(ch)
{
case '+': s.push(s.pop() + s.pop()); break;
case '*': s.push(s.pop() * s.pop()); break;
case '-': s.push(-s.pop() + s.pop()); break;
case '/': s.push(1 / s.pop() * s.pop()); break;
}
}
else if(Character.isDigit(ch))
{
s.push(0.0);
while (Character.isDigit(chars[i]))
s.push(10.0 * s.pop() + (chars[i++] - '0'));
}
}
return s.pop();
}
}
這是我的測試人員:
import java.util.Scanner;
public class ExpressionTester
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
while(true)
{
System.out.println("");
String pf = sc.nextLine();
ExpressionTree eT = new ExpressionTree(pf);
eT.createExpressionTree();
System.out.println("The infix: " + eT.infix() );
System.out.println(eT.evaluate(pf));
}
}
}
任何幫助將不勝感激,因為我真的不知道如何解決此問題,我已經接近完成。
if (isOperator(ch))
{
TreeNode rightNode = nodes.pop();
TreeNode leftNode = nodes.pop();
nodes.push(new TreeNode(leftNode, ch, rightNode));
}
else
{
nodes.add(new TreeNode(null, ch, null));
}
您正在將空格節點放入樹中。 嘗試這個:
if (isOperator(ch))
{
TreeNode rightNode = nodes.pop();
TreeNode leftNode = nodes.pop();
nodes.push(new TreeNode(leftNode, ch, rightNode));
}
else if (!Character.isWhitespace(ch))
{
nodes.add(new TreeNode(null, ch, null));
}
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