Create 面试题 16.26. 计算器.js

Author: yinxin630

面试题 16.26. 计算器.js

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+/**
+ * @param {string} s
+ * @return {number}
+ */
+var calculate = function (s) {
+  const priority = {
+    '+': 1,
+    '-': 2,
+    '*': 3,
+    '/': 3,
+  };
+  function isNumber(charCode) {
+    const ZeroCharCode = '0'.charCodeAt(0);
+    const NineCharCode = '9'.charCodeAt(0);
+    return charCode >= ZeroCharCode && charCode <= NineCharCode;
+  }
+  function isOperator(char) {
+    return ['+', '-', '*', '/'].includes(char);
+  }
+  function getResult(n1, n2, opr) {
+    switch (opr) {
+      case '+': {
+        return n2 + n1;
+        break;
+      }
+      case '-': {
+        return n2 - n1;
+        break;
+      }
+      case '*': {
+        return n2 * n1;
+        break;
+      }
+      case '/': {
+        return Math.floor(n2 / n1);
+        break;
+      }
+    }
+  }
+
+  const numberStack = [];
+  const operatorStack = [];
+  let num = 0;
+  for (let i = 0; i < s.length; i++) {
+    if (isNumber(s.charCodeAt(i))) {
+      num = num * 10 + +s[i];
+      if (i === s.length - 1) {
+        numberStack.push(num);
+      }
+    } else {
+      if (isNumber(s.charCodeAt(i - 1))) {
+        numberStack.push(num);
+        num = 0;
+      }
+
+      if (isOperator(s[i])) {
+        while (
+          operatorStack.length &&
+          priority[operatorStack[operatorStack.length - 1]] >= priority[s[i]]
+        ) {
+          numberStack.push(getResult(numberStack.pop(), numberStack.pop(), operatorStack.pop()));
+        }
+        operatorStack.push(s[i]);
+      }
+    }
+  }
+
+  while (operatorStack.length) {
+    numberStack.push(getResult(numberStack.pop(), numberStack.pop(), operatorStack.pop()));
+  }
+
+  return numberStack[0];
+};