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大家其实百度一下“逆波兰表达式”就可以了~
import java.util.Stack;
public class EvaluateReversePolishNotation {
public static void main(String args[]){
EvaluateReversePolishNotation erp = new EvaluateReversePolishNotation();
String[] tokens = {"3", "-4", "+"};
System.out.println(erp.evalRPN(tokens));
}
public int evalRPN(String[] tokens) {
Stack<Integer> stack = new Stack<Integer>();
int input;
for(int i=0;i<tokens.length;i++){
if(tokens[i].charAt(0)>='0'&&tokens[i].charAt(0)<='9')
{input = Integer.parseInt(tokens[i]);
stack.push(input);
}
else if(tokens[i].length()>1&&tokens[i].charAt(0)=='-'){
input = Integer.parseInt(tokens[i]);
stack.push(input);
}
else if(tokens[i].charAt(0)=='+')
stack.push(stack.pop()+stack.pop());
else if(tokens[i].charAt(0)=='-'){
int tmp = stack.pop();
stack.push(stack.pop()-tmp);
}
else if(tokens[i].charAt(0)=='/'){
int tmp = stack.pop();
stack.push(stack.pop()/tmp);
}
else if(tokens[i].charAt(0)=='*')
stack.push(stack.pop()*stack.pop());
}
return stack.peek();
}
}
【Leetcode】Evaluate Reverse Polish Notation
原文地址：http://blog.csdn.net/qbt4juik/article/details/41543087
