update

hard/224.basic-calculator.go

@@ -1,3 +1,82 @@
+import (
+	"strings"
+	"strconv"
+)
+
 func calculate(s string) int {
-	return 0
+	s = strings.Replace(s, " ", "", -1)
+	nums := make([]int, 0)
+	ops := make([]byte, 0)
+	l, m, n := len(s), 0, 0
+	beg := -1
+	push := false
+	for i := 0; i < l; i++ {
+		switch s[i] {
+		case '+', '-':
+			var num int
+			if beg != -1 {
+				num = atoi(s, beg, i)
+				beg = -1
+			} else {
+				num = nums[n-1]
+				nums = nums[:n-1]
+				n--
+			}
+			if !push && m != 0 { // Pop
+				aopb(&nums[n-1], ops[m-1], num)
+				ops = ops[:m-1]
+				m--
+			} else {
+				nums = append(nums, num)
+				n++
+				push = false
+			}
+			ops = append(ops, s[i])
+			m++
+		case '(':
+			push = true
+		case ')':
+			var num int
+			if beg != -1 {
+				num = atoi(s, beg, i)
+				beg = -1
+			} else {
+				num = nums[n-1]
+				nums = nums[:n-1]
+				n--
+			}
+			if m != 0 { // Handle expressions like (num)
+				aopb(&nums[n-1], ops[m-1], num)
+				ops = ops[:m-1]
+				m--
+			} else {
+				nums = append(nums, num)
+				n++
+			}
+		default: // Case '0', '1', ... , '9'
+			if beg == -1 {
+				beg = i
+			}
+		}
+	}
+	if beg != -1 {
+		nums = append(nums, atoi(s, beg, l))
+	}
+	if len(ops) != 0 {
+		aopb(&nums[0], ops[0], nums[1])
+	}
+	return nums[0]
 }
+
+func atoi(s string, beg, end int) int {
+	i, _ := strconv.Atoi(s[beg:end])
+	return i
+}
+
+func aopb(a *int, op byte, b int) {
+	switch op {
+	case '+': *a += b
+	case '-': *a -= b
+	}
+}
+