Add solution 43、45、73、227

leetcode/0227.Basic-Calculator-II/227. Basic Calculator II.go

@@ -0,0 +1,29 @@
+package leetcode
+
+func calculate(s string) int {
+	stack, preSign, num, res := []int{}, '+', 0, 0
+	for i, ch := range s {
+		isDigit := '0' <= ch && ch <= '9'
+		if isDigit {
+			num = num*10 + int(ch-'0')
+		}
+		if !isDigit && ch != ' ' || i == len(s)-1 {
+			switch preSign {
+			case '+':
+				stack = append(stack, num)
+			case '-':
+				stack = append(stack, -num)
+			case '*':
+				stack[len(stack)-1] *= num
+			default:
+				stack[len(stack)-1] /= num
+			}
+			preSign = ch
+			num = 0
+		}
+	}
+	for _, v := range stack {
+		res += v
+	}
+	return res
+}