题解 | #逆波兰表达式求值#

/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 * 
 * @param tokens string字符串一维数组 
 * @return int整型
 */
function evalRPN( tokens ) {
    // write code here
    let numarr = [];
    for(let i of tokens) {
      // console.log(i);
      // console.log(!isNaN(Number(0)));
      if(!isNaN(Number(i))){
        numarr.push(i)
      }else{
        let tmp;
        let len = numarr.length;
        switch(i) {
          case '+': {
            tmp = Number(numarr[len - 2]) + Number(numarr[len - 1]);
            numarr.pop();
            numarr.pop();
            numarr.push(tmp);
            console.log(tmp);
            break;
          };
          case '-': {
            tmp = Number(numarr[len - 2]) - Number(numarr[len - 1]);
            numarr.pop();
            numarr.pop();
            numarr.push(tmp);
            console.log(tmp);
            break;
          };
          case '*': {
            tmp = Number(numarr[len - 2]) * Number(numarr[len - 1]);
            numarr.pop();
            numarr.pop();
            numarr.push(tmp);
            console.log(tmp);
            break;
          };
          case '/': {
            tmp = parseInt(Number(numarr[len - 2]) / Number(numarr[len - 1]));
            numarr.pop();
            numarr.pop();
            numarr.push(tmp);
            console.log(tmp);
            break;
          };
        }
      }
    }
    return numarr[0];
}
module.exports = {
    evalRPN : evalRPN
};

// 其实只要知道逆波兰表达式是什么就简单了