Evaluate Reverse Polish Notation

标签：数据结构   算法   学习   

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

public class Solution {
    public int evalRPN(String[] tokens) {
        Stack<String> vals=new Stack<String>();
        Stack<String> ops=new Stack<String>();
        for(int i=0;i<tokens.length;i++){
            if( tokens[i].equals("+") || tokens[i].equals("-") || tokens[i].equals("*") || tokens[i].equals("/")  ){
                ops.push(tokens[i]);
                while(!ops.empty() && !vals.empty()){
                    String op=ops.pop();
                    String val=vals.pop();
                    int d=Integer.parseInt(val);
                    if(op.equals("+")) {
                    	d=Integer.parseInt(vals.pop()) + d;
                    }
                    else if(op.equals("-")){
                    	d=Integer.parseInt(vals.pop()) - d;
                    }
                    else if(op.equals("*")){
                    	d=Integer.parseInt(vals.pop()) * d;
                    }
                    else if(op.equals("/")){
                    	d=Integer.parseInt(vals.pop()) / d;
                    }
                    new String();
					vals.push(String.valueOf(d));
                }
            }
            else{
                vals.push(tokens[i]);
            }
        }
        return Integer.parseInt(vals.pop());
    }
}

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Evaluate Reverse Polish Notation

标签：数据结构   算法   学习   

原文地址：http://blog.csdn.net/dutsoft/article/details/37698321