Create 772-basic-calculator-iii.js

Author: everthis

772-basic-calculator-iii.js

@@ -0,0 +1,62 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+const calculate = function (
+  s,
+  start = 0,
+  end = s.length,
+  parentheses = findParentheses(s)
+) {
+  const stack = []
+  let op = '+'
+  let num = 0
+  for (let i = start; i < end; i++) {
+    const c = s[i]
+    if (/[0-9]+/.test(c)) {
+      const n = parseInt(c)
+      num = 10 * num + n
+    } else if (isOperator(c)) {
+      compute(op, stack, num)
+      op = c
+      num = 0
+    } else if (c === '(') {
+      num = calculate(s, i + 1, parentheses[i], parentheses)
+      i = parentheses[i]
+    }
+  }
+  compute(op, stack, num)
+  return stack.reduce((acc, cur) => acc + cur, 0)
+}
+
+function findParentheses(s) {
+  const map = {}
+  const stack = []
+  for (let i = 0; i < s.length; i++) {
+    if (s[i] === '(') {
+      stack.push(i)
+    } else if (s[i] === ')') {
+      map[stack.pop()] = i
+    }
+  }
+  return map
+}
+
+function compute(op, stack, num) {
+  if (op === '-') {
+    stack.push(-num)
+  } else if (op === '+') {
+    stack.push(num)
+  } else if (op === '*') {
+    stack.push(stack.pop() * num)
+  } else if (op === '/') {
+    const pre = stack.pop()
+    const sign = pre / num >= 0 ? 1 : -1
+    const val = Math.floor(Math.abs(pre / num))
+    stack.push(Math.floor(sign * val))
+  }
+}
+
+function isOperator(c) {
+  return c === '+' || c === '-' || c === '*' || c === '/'
+}