150. 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.
Note:
- Division between two integers should truncate toward zero.
- The given RPN expression is always valid. That means the expression would always evaluate to a result and there won't be any divide by zero operation.
Example 1:
Input: ["2", "1", "+", "3", "*"] Output: 9 Explanation: ((2 + 1) * 3) = 9
Example 2:
Input: ["4", "13", "5", "/", "+"] Output: 6 Explanation: (4 + (13 / 5)) = 6
Example 3:
Input: ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"] Output: 22 Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5 = ((10 * (6 / (12 * -11))) + 17) + 5 = ((10 * (6 / -132)) + 17) + 5 = ((10 * 0) + 17) + 5 = (0 + 17) + 5 = 17 + 5 = 22
题意:运算一个表达式,给定一个数组,操作符紧跟数字后面
代码如下:
/** * @param {string[]} tokens * @return {number} */ var evalRPN = function(tokens) { let option=[] if(tokens.length===1) return tokens.pop(); for(let i=0;i<tokens.length;i++){ let num1,num2; if(tokens[i]!=='+' && tokens[i]!=='-' && tokens[i]!=='*' && tokens[i]!=='/'){ option.push(tokens[i]); }else{ num1=parseInt(option.pop()); num2=parseInt(option.pop()); switch(tokens[i]){ case '+': option.push(num2+num1) break; case '-': option.push(num2-num1) break; case '*': option.push(num2*num1) break; case '/': option.push(parseInt(num2/num1)) break; } } } return option.pop(); };