[LeetCode][JavaScript]Evaluate Reverse Polish Notation

Evaluate Reverse Polish Notation

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

https://leetcode.com/problems/evaluate-reverse-polish-notation/

 

 

 

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逆波兰表达式，也就是后缀表达式，做过两道更难的题之后，这题秒了。

http://www.cnblogs.com/Liok3187/p/4564877.html

http://www.cnblogs.com/Liok3187/p/4593365.html

/**
 * @param {string[]} tokens
 * @return {number}
 */
var evalRPN = function(tokens) {
    var resStack = [];
    var opStack = [];
    var right, left;
    for(var i  = 0; i < tokens.length; i++){
        var curr = tokens[i];
        if(/^(\+|\-|\/|\*)$/.test(curr)){
            right = resStack.pop();
            left = resStack.pop();
            if(curr === '+'){
                resStack.push(left + right);
            }else if(curr === '-'){
                resStack.push(left - right);
            }else if(curr === '/'){
                resStack.push(parseInt(left / right));
            }else if(curr === '*'){
                resStack.push(left * right);
            }
        }else{
            resStack.push(parseInt(curr));    
        }
    }
    return resStack[0];
};