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‎Problemset/0224-Basic Calculator/README.md

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# 224. Basic Calculator
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Given a string `s` representing a valid expression, implement a basic calculator to evaluate it, and return *the result of the evaluation*.
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**Note:** You are **not** allowed to use any built-in function which evaluates strings as mathematical expressions, such as `eval()`.
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#### Example 1:
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<pre>
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<strong>Input:</strong> s = "1 + 1"
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<strong>Output:</strong> 2
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</pre>
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#### Example 2:
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<pre>
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<strong>Input:</strong> s = " 2-1 + 2 "
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<strong>Output:</strong> 3
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</pre>
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#### Example 3:
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<pre>
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<strong>Input:</strong> s = "(1+(4+5+2)-3)+(6+8)"
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<strong>Output:</strong> 23
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</pre>
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#### Constraints:
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* <code>1 <= s.length <= 3 * 10<sup>5</sup></code>
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* `s` consists of digits, `'+'`, `'-'`, `'('`, `')'`, and `' '`.
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* `s` represents a valid expression.
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* `'+'` is **not** used as a unary operation (i.e., `"+1"` and `"+(2 + 3)"` is invalid).
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* `'-'` could be used as a unary operation (i.e., `"-1"` and `"-(2 + 3)"` is valid).
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* There will be no two consecutive operators in the input.
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* Every number and running calculation will fit in a signed 32-bit integer.
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## Solutions (Python)
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### 1. Solution
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```Python
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class Solution:
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def calculate(self, s: str) -> int:
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s = s.replace(' ', '')
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negstack = [False]
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stack = []
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ret = 0
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for i in range(len(s)):
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if s[i] == '(':
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if i == 0 or s[i - 1] != '-':
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negstack.append(negstack[-1])
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else:
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negstack.append(not negstack[-1])
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elif s[i] == ')':
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negstack.pop()
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elif s[i] == '+':
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stack.append('-' if negstack[-1] else '+')
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elif s[i] == '-':
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if stack == [] or isinstance(stack[-1], str):
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stack.append(0)
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stack.append('+' if negstack[-1] else '-')
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else:
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if stack == [] or isinstance(stack[-1], str):
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stack.append(0)
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stack[-1] = stack[-1] * 10 + int(s[i])
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ret = stack[0]
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for i in range(2, len(stack), 2):
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ret += stack[i] if stack[i - 1] == '+' else -stack[i]
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return ret
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```

‎Problemset/0224-Basic Calculator/README_CN.md

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# 224. 基本计算器
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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。
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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()` 。
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#### 示例 1:
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<pre>
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<strong>输入:</strong> s = "1 + 1"
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<strong>输出:</strong> 2
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</pre>
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#### 示例 2:
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<pre>
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<strong>输入:</strong> s = " 2-1 + 2 "
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<strong>输出:</strong> 3
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</pre>
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#### 示例 3:
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<pre>
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<strong>输入:</strong> s = "(1+(4+5+2)-3)+(6+8)"
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<strong>输出:</strong> 23
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</pre>
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#### 提示:
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* <code>1 <= s.length <= 3 * 10<sup>5</sup></code>
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* `s` 由数字、`'+'`、`'-'`、`'('`、`')'`、和 `' '` 组成
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* `s` 表示一个有效的表达式
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* `'+'` 不能用作一元运算(例如， `"+1"` 和 `"+(2 + 3)"` 无效)
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* `'-'` 可以用作一元运算(即 `"-1"` 和 `"-(2 + 3)"` 是有效的)
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* 输入中不存在两个连续的操作符
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* 每个数字和运行的计算将适合于一个有符号的 32位 整数
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## 题解 (Python)
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### 1. 题解
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```Python
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class Solution:
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def calculate(self, s: str) -> int:
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s = s.replace(' ', '')
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negstack = [False]
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stack = []
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ret = 0
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for i in range(len(s)):
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if s[i] == '(':
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if i == 0 or s[i - 1] != '-':
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negstack.append(negstack[-1])
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else:
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negstack.append(not negstack[-1])
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elif s[i] == ')':
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negstack.pop()
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elif s[i] == '+':
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stack.append('-' if negstack[-1] else '+')
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elif s[i] == '-':
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if stack == [] or isinstance(stack[-1], str):
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stack.append(0)
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stack.append('+' if negstack[-1] else '-')
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else:
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if stack == [] or isinstance(stack[-1], str):
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stack.append(0)
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stack[-1] = stack[-1] * 10 + int(s[i])
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ret = stack[0]
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for i in range(2, len(stack), 2):
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ret += stack[i] if stack[i - 1] == '+' else -stack[i]
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return ret
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```

‎Problemset/0224-Basic Calculator/Solution.py

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class Solution:
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def calculate(self, s: str) -> int:
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s = s.replace(' ', '')
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negstack = [False]
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stack = []
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ret = 0
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for i in range(len(s)):
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if s[i] == '(':
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if i == 0 or s[i - 1] != '-':
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negstack.append(negstack[-1])
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else:
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negstack.append(not negstack[-1])
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elif s[i] == ')':
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negstack.pop()
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elif s[i] == '+':
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stack.append('-' if negstack[-1] else '+')
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elif s[i] == '-':
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if stack == [] or isinstance(stack[-1], str):
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stack.append(0)
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stack.append('+' if negstack[-1] else '-')
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else:
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if stack == [] or isinstance(stack[-1], str):
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stack.append(0)
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stack[-1] = stack[-1] * 10 + int(s[i])
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ret = stack[0]
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for i in range(2, len(stack), 2):
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ret += stack[i] if stack[i - 1] == '+' else -stack[i]
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return ret

‎README.md

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[221][221l] |[Maximal Square][221] |![rs]
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[222][222l] |[Count Complete Tree Nodes][222] |![py]
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[223][223l] |[Rectangle Area][223] |![rb]&nbsp;&nbsp;![rs]
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[224][224l] |[Basic Calculator][224] |![py]
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[225][225l] |[Implement Stack using Queues][225] |![rs]
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[226][226l] |[Invert Binary Tree][226] |![py]
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[227][227l] |[Basic Calculator II][227] |![py]
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[221]:Problemset/0221-Maximal%20Square/README.md#221-maximal-square
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[222]:Problemset/0222-Count%20Complete%20Tree%20Nodes/README.md#222-count-complete-tree-nodes
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[223]:Problemset/0223-Rectangle%20Area/README.md#223-rectangle-area
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[224]:Problemset/0224-Basic%20Calculator/README.md#224-basic-calculator
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[225]:Problemset/0225-Implement%20Stack%20using%20Queues/README.md#225-implement-stack-using-queues
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[226]:Problemset/0226-Invert%20Binary%20Tree/README.md#226-invert-binary-tree
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[227]:Problemset/0227-Basic%20Calculator%20II/README.md#227-basic-calculator-ii
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[221l]:https://leetcode.com/problems/maximal-square/
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[222l]:https://leetcode.com/problems/count-complete-tree-nodes/
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[223l]:https://leetcode.com/problems/rectangle-area/
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[224l]:https://leetcode.com/problems/basic-calculator/
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[225l]:https://leetcode.com/problems/implement-stack-using-queues/
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[226l]:https://leetcode.com/problems/invert-binary-tree/
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[227l]:https://leetcode.com/problems/basic-calculator-ii/

‎README_CN.md

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[221][221l] |[最大正方形][221] |![rs]
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[222][222l] |[完全二叉树的节点个数][222] |![py]
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[223][223l] |[矩形面积][223] |![rb]&nbsp;&nbsp;![rs]
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[224][224l] |[基本计算器][224] |![py]
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[225][225l] |[用队列实现栈][225] |![rs]
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[226][226l] |[翻转二叉树][226] |![py]
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[227][227l] |[基本计算器 II][227] |![py]
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[221]:Problemset/0221-Maximal%20Square/README_CN.md#221-最大正方形
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[222]:Problemset/0222-Count%20Complete%20Tree%20Nodes/README_CN.md#222-完全二叉树的节点个数
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[223]:Problemset/0223-Rectangle%20Area/README_CN.md#223-矩形面积
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[224]:Problemset/0224-Basic%20Calculator/README_CN.md#224-基本计算器
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[225]:Problemset/0225-Implement%20Stack%20using%20Queues/README_CN.md#225-用队列实现栈
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[226]:Problemset/0226-Invert%20Binary%20Tree/README_CN.md#226-翻转二叉树
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[227]:Problemset/0227-Basic%20Calculator%20II/README_CN.md#227-基本计算器-ii
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[221l]:https://leetcode.cn/problems/maximal-square/
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[222l]:https://leetcode.cn/problems/count-complete-tree-nodes/
35423544
[223l]:https://leetcode.cn/problems/rectangle-area/
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[224l]:https://leetcode.cn/problems/basic-calculator/
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[225l]:https://leetcode.cn/problems/implement-stack-using-queues/
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[226l]:https://leetcode.cn/problems/invert-binary-tree/
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[227l]:https://leetcode.cn/problems/basic-calculator-ii/

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