Question Definition
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
Some examples:
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9
["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
Java Solution
public int evalRPN(String[] tokens) {
Deque<Integer> stack = new ArrayDeque<>();
int result = 0;
for(String token : tokens){
if(token.equals("+")){
stack.push(stack.poll() + stack.poll());
}else if(token.equals("-")){
int num = stack.poll();
stack.push(stack.poll() - num);
}else if(token.equals("*")){
stack.push(stack.poll() * stack.poll());
}else if(token.equals("/")){
int num = stack.poll();
stack.push(stack.poll() / num);
}else {
stack.push(Integer.parseInt(token));
}
}
return stack.poll();
}
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