Menilai ungkapan matematik dengan mengambil kira operator keutamaan dalam JavaScript-tutorial js-php.cn

Menilai ungkapan matematik dengan mengambil kira operator keutamaan dalam JavaScript

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Lepaskan： 2023-08-24 15:53:09

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Soalan

Kita perlu menulis fungsi JavaScript yang menerima ungkapan matematik sebagai rentetan dan mengembalikan hasilnya sebagai nombor.

Kita perlu menyokong pengendali matematik berikut -

Pembahagian / (sebagai pembahagian titik terapung)
Tambahan + p>
Penolakan -
Penolakan -

Operator sentiasa berdasarkan kiri Ke kanan, * dan / mesti dinilai sebelum + dan -.

Contoh

Berikut ialah kod -

Demonstrasi masa nyata

const exp = &#39;6 - 4&#39;;
const findResult = (exp = &#39;&#39;) => {
   const digits = &#39;0123456789.&#39;;
   const operators = [&#39;+&#39;, &#39;-&#39;, &#39;*&#39;, &#39;/&#39;, &#39;negate&#39;];
   const legend = {
      &#39;+&#39;: { pred: 2, func: (a, b) => { return a + b; }, assoc: "left" },
      &#39;-&#39;&: { pred: 2, func: (a, b) => { return a - b; }, assoc: "left" },
      &#39;*&#39;: { pred: 3, func: (a, b) => { return a * b; }, assoc: "left" },
      &#39;/&#39;: { pred: 3, func: (a, b) => {
      if (b != 0) { return a / b; } else { return 0; }
   }
   }, assoc: "left",
   &#39;negate&#39;: { pred: 4, func: (a) => { return -1 * a; }, assoc: "right" }
};
exp = exp.replace(/\s/g, &#39;&#39;);
let operations = [];
let outputQueue = [];
let ind = 0;
let str = &#39;&#39;;
while (ind < exp.length) {
   let ch = exp[ind];
   if (operators.includes(ch)) {
      if (str !== &#39;&#39;) {
         outputQueue.push(new Number(str));
         str = &#39;&#39;;
      }
      if (ch === &#39;-&#39;) {
         if (ind == 0) {
            ch = &#39;negate&#39;;
         } else {
            let nextCh = exp[ind+1];
            let prevCh = exp[ind-1];
            if ((digits.includes(nextCh) || nextCh === &#39;(&#39; || nextCh === &#39;-&#39;) &&
               (operators.includes(prevCh) || exp[ind-1] === &#39;(&#39;)) {
                  ch = &#39;negate&#39;;
            }
         }
      }
      if (operations.length > 0) {
         let topOper = operations[operations.length - 1];
         while (operations.length > 0 && legend[topOper] &&
         ((legend[ch].assoc === &#39;left&#39; && legend[ch].pred <= legend[topOper].pred) ||
         (legend[ch].assoc === &#39;right&#39; && legend[ch].pred < legend[topOper].pred))) {
            outputQueue.push(operations.pop());
            topOper = operations[operations.length - 1];
         }
      }
      operations.push(ch);
   } else if (digits.includes(ch)) {
      str += ch
   } else if (ch === &#39;(&#39;) {
      operations.push(ch);
   } else if (ch === &#39;)&#39;) {
      if (str !== &#39;&#39;) {
         outputQueue.push(new Number(str));
         str = &#39;&#39;;
      }
      while (operations.length > 0 && operations[operations.length - 1] !== &#39;(&#39;) {
         outputQueue.push(operations.pop());
      }
      if (operations.length > 0) { operations.pop(); }
   }
   ind++;
}
if (str !== &#39;&#39;) { outputQueue.push(new Number(str)); }
   outputQueue = outputQueue.concat(operations.reverse())
   let res = [];
   while (outputQueue.length > 0) {
      let ch = outputQueue.shift();
      if (operators.includes(ch)) {
         let num1, num2, subResult;
         if (ch === &#39;negate&#39;) {
            res.push(legend[ch].func(res.pop()));
         } else {
            let [num2, num1] = [res.pop(), res.pop()];
            res.push(legend[ch].func(num1, num2));
         }
      } else {
         res.push(ch);
      }
   }
   return res.pop().valueOf();
};
console.log(findResult(exp));

Salin selepas log masuk

Output

Salin selepas log masuk

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