+ problem 227

fruit-in · fruit-in · commit 534f2ff55145 · 2023-11-16T22:24:53.000+08:00
diff --git a/Problemset/0227-Basic Calculator II/README.md b/Problemset/0227-Basic Calculator II/README.md
@@ -0,0 +1,84 @@
+# 227. Basic Calculator II
+Given a string `s` which represents an expression, *evaluate this expression and return its value*.
+
+The integer division should truncate toward zero.
+
+You may assume that the given expression is always valid. All intermediate results will be in the range of <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>.
+
+**Note:** You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as `eval()`.
+
+#### Example 1:
+<pre>
+<strong>Input:</strong> s = "3+2*2"
+<strong>Output:</strong> 7
+</pre>
+
+#### Example 2:
+<pre>
+<strong>Input:</strong> s = " 3/2 "
+<strong>Output:</strong> 1
+</pre>
+
+#### Example 3:
+<pre>
+<strong>Input:</strong> s = " 3+5 / 2 "
+<strong>Output:</strong> 5
+</pre>
+
+#### Constraints:
+* <code>1 <= s.length <= 3 * 10<sup>5</sup></code>
+* `s` consists of integers and operators `('+', '-', '*', '/')` separated by some number of spaces.
+* `s` represents **a valid expression**.
+* All the integers in the expression are non-negative integers in the range <code>[0, 2<sup>31</sup> - 1]</code>.
+* The answer is **guaranteed** to fit in a **32-bit integer**.
+
+## Solutions (Python)
+
+### 1. Solution
+```Python
+class Solution:
+    def calculate(self, s: str) -> int:
+        isint = False
+        lastsign = None
+        stack = []
+        ret = 0
+
+        for ch in s:
+            if ch in "+-*/":
+                if lastsign == '*':
+                    x, _ = stack.pop(), stack.pop()
+                    stack[-1] *= x
+                elif lastsign == '/':
+                    x, _ = stack.pop(), stack.pop()
+                    stack[-1] //= x
+
+                isint = False
+                lastsign = ch
+                stack.append(ch)
+            elif ch.isdigit():
+                if isint:
+                    stack[-1] = stack[-1] * 10 + int(ch)
+                else:
+                    isint = True
+                    stack.append(int(ch))
+
+        if lastsign == '*':
+            x, _ = stack.pop(), stack.pop()
+            stack[-1] *= x
+        elif lastsign == '/':
+            x, _ = stack.pop(), stack.pop()
+            stack[-1] //= x
+
+        lastsign = '+'
+
+        for elem in stack:
+            if isinstance(elem, int):
+                if lastsign == '+':
+                    ret += elem
+                elif lastsign == '-':
+                    ret -= elem
+            else:
+                lastsign = elem
+
+        return ret
+```
diff --git a/Problemset/0227-Basic Calculator II/README_CN.md b/Problemset/0227-Basic Calculator II/README_CN.md
@@ -0,0 +1,84 @@
+# 227. 基本计算器 II
+给你一个字符串表达式 `s` ，请你实现一个基本计算器来计算并返回它的值。
+
+整数除法仅保留整数部分。
+
+你可以假设给定的表达式总是有效的。所有中间结果将在 <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code> 的范围内。
+
+**注意：**不允许使用任何将字符串作为数学表达式计算的内置函数，比如 `eval()` 。
+
+#### 示例 1:
+<pre>
+<strong>输入:</strong> s = "3+2*2"
+<strong>输出:</strong> 7
+</pre>
+
+#### 示例 2:
+<pre>
+<strong>输入:</strong> s = " 3/2 "
+<strong>输出:</strong> 1
+</pre>
+
+#### 示例 3:
+<pre>
+<strong>输入:</strong> s = " 3+5 / 2 "
+<strong>输出:</strong> 5
+</pre>
+
+#### 提示:
+* <code>1 <= s.length <= 3 * 10<sup>5</sup></code>
+* `s` 由整数和算符 `('+', '-', '*', '/')` 组成，中间由一些空格隔开
+* `s` 表示一个 **有效表达式**
+* 表达式中的所有整数都是非负整数，且在范围 <code>[0, 2<sup>31</sup> - 1]</code> 内
+* 题目数据保证答案是一个 **32-bit 整数**
+
+## 题解 (Python)
+
+### 1. 题解
+```Python
+class Solution:
+    def calculate(self, s: str) -> int:
+        isint = False
+        lastsign = None
+        stack = []
+        ret = 0
+
+        for ch in s:
+            if ch in "+-*/":
+                if lastsign == '*':
+                    x, _ = stack.pop(), stack.pop()
+                    stack[-1] *= x
+                elif lastsign == '/':
+                    x, _ = stack.pop(), stack.pop()
+                    stack[-1] //= x
+
+                isint = False
+                lastsign = ch
+                stack.append(ch)
+            elif ch.isdigit():
+                if isint:
+                    stack[-1] = stack[-1] * 10 + int(ch)
+                else:
+                    isint = True
+                    stack.append(int(ch))
+
+        if lastsign == '*':
+            x, _ = stack.pop(), stack.pop()
+            stack[-1] *= x
+        elif lastsign == '/':
+            x, _ = stack.pop(), stack.pop()
+            stack[-1] //= x
+
+        lastsign = '+'
+
+        for elem in stack:
+            if isinstance(elem, int):
+                if lastsign == '+':
+                    ret += elem
+                elif lastsign == '-':
+                    ret -= elem
+            else:
+                lastsign = elem
+
+        return ret
+```
diff --git a/Problemset/0227-Basic Calculator II/Solution.py b/Problemset/0227-Basic Calculator II/Solution.py
@@ -0,0 +1,45 @@
+class Solution:
+    def calculate(self, s: str) -> int:
+        isint = False
+        lastsign = None
+        stack = []
+        ret = 0
+
+        for ch in s:
+            if ch in "+-*/":
+                if lastsign == '*':
+                    x, _ = stack.pop(), stack.pop()
+                    stack[-1] *= x
+                elif lastsign == '/':
+                    x, _ = stack.pop(), stack.pop()
+                    stack[-1] //= x
+
+                isint = False
+                lastsign = ch
+                stack.append(ch)
+            elif ch.isdigit():
+                if isint:
+                    stack[-1] = stack[-1] * 10 + int(ch)
+                else:
+                    isint = True
+                    stack.append(int(ch))
+
+        if lastsign == '*':
+            x, _ = stack.pop(), stack.pop()
+            stack[-1] *= x
+        elif lastsign == '/':
+            x, _ = stack.pop(), stack.pop()
+            stack[-1] //= x
+
+        lastsign = '+'
+
+        for elem in stack:
+            if isinstance(elem, int):
+                if lastsign == '+':
+                    ret += elem
+                elif lastsign == '-':
+                    ret -= elem
+            else:
+                lastsign = elem
+
+        return ret
diff --git a/README.md b/README.md
@@ -156,6 +156,7 @@
 [223][223l]  |[Rectangle Area][223]                                                                 |![rb]&nbsp;&nbsp;![rs]
 [225][225l]  |[Implement Stack using Queues][225]                                                   |![rs]
 [226][226l]  |[Invert Binary Tree][226]                                                             |![py]
+[227][227l]  |[Basic Calculator II][227]                                                            |![py]
 [228][228l]  |[Summary Ranges][228]                                                                 |![py]
 [229][229l]  |[Majority Element II][229]                                                            |![rs]
 [230][230l]  |[Kth Smallest Element in a BST][230]                                                  |![rb]
@@ -1435,6 +1436,7 @@
 [223]:Problemset/0223-Rectangle%20Area/README.md#223-rectangle-area
 [225]:Problemset/0225-Implement%20Stack%20using%20Queues/README.md#225-implement-stack-using-queues
 [226]:Problemset/0226-Invert%20Binary%20Tree/README.md#226-invert-binary-tree
+[227]:Problemset/0227-Basic%20Calculator%20II/README.md#227-basic-calculator-ii
 [228]:Problemset/0228-Summary%20Ranges/README.md#228-summary-ranges
 [229]:Problemset/0229-Majority%20Element%20II/README.md#229-majority-element-ii
 [230]:Problemset/0230-Kth%20Smallest%20Element%20in%20a%20BST/README.md#230-kth-smallest-element-in-a-bst
@@ -2711,6 +2713,7 @@
 [223l]:https://leetcode.com/problems/rectangle-area/
 [225l]:https://leetcode.com/problems/implement-stack-using-queues/
 [226l]:https://leetcode.com/problems/invert-binary-tree/
+[227l]:https://leetcode.com/problems/basic-calculator-ii/
 [228l]:https://leetcode.com/problems/summary-ranges/
 [229l]:https://leetcode.com/problems/majority-element-ii/
 [230l]:https://leetcode.com/problems/kth-smallest-element-in-a-bst/
diff --git a/README_CN.md b/README_CN.md
@@ -156,6 +156,7 @@
 [223][223l]  |[矩形面积][223]                                           |![rb]&nbsp;&nbsp;![rs]
 [225][225l]  |[用队列实现栈][225]                                       |![rs]
 [226][226l]  |[翻转二叉树][226]                                         |![py]
+[227][227l]  |[基本计算器 II][227]                                      |![py]
 [228][228l]  |[汇总区间][228]                                           |![py]
 [229][229l]  |[多数元素 II][229]                                        |![rs]
 [230][230l]  |[二叉搜索树中第K小的元素][230]                            |![rb]
@@ -1435,6 +1436,7 @@
 [223]:Problemset/0223-Rectangle%20Area/README_CN.md#223-矩形面积
 [225]:Problemset/0225-Implement%20Stack%20using%20Queues/README_CN.md#225-用队列实现栈
 [226]:Problemset/0226-Invert%20Binary%20Tree/README_CN.md#226-翻转二叉树
+[227]:Problemset/0227-Basic%20Calculator%20II/README_CN.md#227-基本计算器-ii
 [228]:Problemset/0228-Summary%20Ranges/README_CN.md#228-汇总区间
 [229]:Problemset/0229-Majority%20Element%20II/README_CN.md#229-多数元素-ii
 [230]:Problemset/0230-Kth%20Smallest%20Element%20in%20a%20BST/README_CN.md#230-二叉搜索树中第k小的元素
@@ -2711,6 +2713,7 @@
 [223l]:https://leetcode.cn/problems/rectangle-area/
 [225l]:https://leetcode.cn/problems/implement-stack-using-queues/
 [226l]:https://leetcode.cn/problems/invert-binary-tree/
+[227l]:https://leetcode.cn/problems/basic-calculator-ii/
 [228l]:https://leetcode.cn/problems/summary-ranges/
 [229l]:https://leetcode.cn/problems/majority-element-ii/
 [230l]:https://leetcode.cn/problems/kth-smallest-element-in-a-bst/
