package com.coding.basic.stack.expression;
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
public class InfixToPostfix {
public static List<Token> convert(String expr) {
TokenParser parser = new TokenParser();
List<Token> tokens = parser.parse(expr);
Stack<Token> opStack = new Stack<>();
Stack<Token> numStack = new Stack<>();
for (Token token : tokens) {
if(token.isNumber()){
numStack.push(token);
}
if(token.isOperator()){
if(opStack.isEmpty()){
opStack.push(token);
} else {
Token pre = opStack.peek();
if(token.hasHigherPriority(pre)){
opStack.push(token);
} else {
while(!opStack.isEmpty()){
numStack.push(opStack.pop());
}
opStack.push(token);
}
}
}
}
List<Token> temp = new ArrayList<>();
while(!numStack.isEmpty()){
temp.add(numStack.pop());
}
List<Token> result = new ArrayList<>();
for(int i = temp.size()-1; i >= 0; i--){
result.add(temp.get(i));
}
return result;
}
}