[Swift]LeetCode227. 基本计算器 II | Basic Calculator II
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➤微信公众号：山青咏芝（shanqingyongzhi）
➤博客园地址：山青咏芝（https://www.cnblogs.com/strengthen/）
➤GitHub地址：https://github.com/strengthen/LeetCode
➤原文地址：https://www.cnblogs.com/strengthen/p/10204363.html
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Implement a basic calculator to evaluate a simple expression string.
The expression string contains only non-negative integers, +, -, *, /operators and empty spaces . The integer division should truncate toward zero.
Example 1:
Input: "3+2*2" Output: 7
Example 2:
Input: " 3/2 " Output: 1
Example 3:
Input: " 3+5 / 2 " Output: 5
Note:
- You may assume that the given expression is always valid.
- Do not use the
evalbuilt-in library function.
实现一个基本的计算器来计算一个简单的字符串表达式的值。
字符串表达式仅包含非负整数，+， - ，*，/ 四种运算符和空格 。 整数除法仅保留整数部分。
示例 1:
输入: "3+2*2" 输出: 7
示例 2:
输入: " 3/2 " 输出: 1
示例 3:
输入: " 3+5 / 2 " 输出: 5
说明：
- 你可以假设所给定的表达式都是有效的。
- 请不要使用内置的库函数
eval。
116ms
1 class Solution {
2 func calculate(_ s: String) -> Int {
3 var num = 0
4 var sign = "+"
5 var strArr = Array(s)
6 var stack = [Int]()
7 var res = 0
8
9 for i in 0..<strArr.count {
10 if strArr[i] >= "0" && strArr[i] <= "9" {
11 num = num * 10 + Int(String(strArr[i]))!
12 }
13
14 if ((strArr[i] < "0" || strArr[i] > "9") && strArr[i] != " ") || i == strArr.count - 1 {
15 if sign == "+" {
16 stack.append(num)
17 } else if sign == "-" {
18 stack.append(-num)
19 } else if sign == "*" {
20 stack.append(stack.removeLast() * num)
21 } else if sign == "/" {
22 stack.append(stack.removeLast() / num)
23 }
24
25 sign = String(strArr[i])
26 num = 0
27 }
28 }
29
30
31 for i in stack {
32 res += i
33 }
34
35 return res
36 }
37 }124ms
1 class Solution {
2 func calculate(_ s: String) -> Int {
3 var stack = [Int]()
4 var str = Array(s+"+")
5
6 var num = 0
7 var sign: Character = "+"
8
9 for char in str {
10 if char >= "0" && char <= "9" {
11 num = num * 10 + Int(String(char))!
12 } else if operators.contains(char) {
13 if sign == "+" || sign == "-"{
14 stack.append((sign == "-" ? -1 : 1) * num)
15 } else if sign == "*" || sign == "/" {
16 let n = stack.removeLast()
17 stack.append(sign == "*" ? n * num : n / num)
18 }
19 num = 0
20 sign = char
21 }
22 }
23 return stack.reduce(0, +)
24 }
25
26 let operators = Set<Character>(["+", "-", "*", "/"])
27 }140ms
1 class Solution {
2 func calculate(_ s: String) -> Int {
3 var stack = [Int]()
4 var str = Array(s+"+")
5
6 var num = 0
7 var sign: Character = "+"
8
9 for char in str {
10 if operands.contains(char) {
11 num = num * 10 + Int(String(char))!
12 } else if operators.contains(char) {
13 if sign == "+" || sign == "-"{
14 stack.append((sign == "-" ? -1 : 1) * num)
15 } else if sign == "*" || sign == "/" {
16 let n = stack.removeLast()
17 stack.append(sign == "*" ? n * num : n / num)
18 }
19 num = 0
20 sign = char
21 }
22 }
23 return stack.reduce(0, +)
24 }
25
26 let operators = Set<Character>(["+", "-", "*", "/"])
27 let operands = Set<Character>(["0", "1", "2", "3", "4", "5", "6", "7", "8", "9"])
28 }228ms
1 class Solution {
2 func calculate(_ s: String) -> Int {
3 var nums: [Int] = []
4 var operations: [Character] = []
5 var preNum = ""
6 for char in s {
7 if let _ = Int(String(char)) {
8 preNum += String(char)
9 } else {
10 if preNum != "" {
11 nums.append(Int(preNum)!)
12 preNum = ""
13 }
14
15 if !operations.isEmpty {
16 let operation = operations[operations.count - 1]
17 if nums.count > operations.count && (operation == "*" || operation == "/") {
18 let num2 = nums.popLast()!
19 let num1 = nums.popLast()!
20 if operation == "*" {
21 let num = num1 * num2
22 nums.append(num)
23 } else if operation == "/" {
24 let num = num1 / num2
25 nums.append(num)
26 }
27
28 operations.removeLast()
29 }
30 }
31
32
33 if char != " " {
34 operations.append(char)
35 }
36 }
37 }
38
39 if preNum != "" {
40 nums.append(Int(preNum)!)
41 }
42
43 if !operations.isEmpty && operations.last == "/" || operations.last == "*" {
44 let operation = operations.popLast()!
45 let num2 = nums.popLast()!
46 let num1 = nums.popLast()!
47 if operation == "*" {
48 nums.append(num1 * num2)
49 } else if operation == "/" {
50 nums.append(num1 / num2)
51 }
52 }
53
54 nums.reverse()
55 for operation in operations {
56 let num1 = nums.popLast()!
57 let num2 = nums.popLast()!
58 if operation == "+" {
59 nums.append(num1 + num2)
60 } else if operation == "-" {
61 nums.append(num1 - num2)
62 } else if operation == "*" {
63 nums.append(num1 * num2)
64 } else if operation == "/" {
65 nums.append(num1 / num2)
66 }
67 }
68
69 return nums.isEmpty ? 0 : nums[0]
70 }
71 }548ms
1 class Solution {
2 func calculate(_ s: String) -> Int {
3 var numStack = [Int]()
4 var opeStack = [String]()
5 let sArr = Array(s)
6 let nums = "0123456789"
7 let opes = "+-*/"
8
9 var i = 0
10 while i < sArr.count {
11 let c = sArr[i]
12 if nums.contains(c) {
13 var tmp = 0
14 while i < sArr.count && nums.contains(sArr[i]) {
15 tmp = tmp * 10 + Int(String(sArr[i]))!
16 i += 1
17 }
18 if let ope = opeStack.last, ope == "*" || ope == "/" {
19 let last = numStack.removeLast()
20 opeStack.removeLast()
21 if ope == "*" {
22 tmp *= last
23 }else if ope == "/" {
24 tmp = last / tmp
25 }
26
27 }
28 numStack.append(tmp)
29 i -= 1
30 }else if opes.contains(c) {
31 opeStack.append(String(c))
32 }
33
34 i += 1
35 }
36
37 var res = numStack.first ?? 0
38
39 for i in 0..<opeStack.count {
40 let ope = opeStack[i]
41 if ope == "+" {
42 res += numStack[i+1]
43 }else if ope == "-" {
44 res -= numStack[i+1]
45 }
46 }
47 return res
48 }
49 }转载于:https://www.cnblogs.com/strengthen/p/10204363.html
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