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Merge pull request #22 from tiationg-kho/update
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‎README.md

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@@ -312,14 +312,14 @@ Pattern500 is inspired by Blind 75 and Grind 75's classic problem selection. Pat
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| 298 | | [346. Moving Average from Data Stream](https://leetcode.com/problems/moving-average-from-data-stream/) | [I]stack-queue | use queue to simulate | [Python]([I]stack-queue/[I]stack-queue/346-moving-average-from-data-stream.py) |
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| 299 | O | [20. Valid Parentheses](https://leetcode.com/problems/valid-parentheses/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/20-valid-parentheses.py) |
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| 300 | O | [150. Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/150-evaluate-reverse-polish-notation.py) |
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| 301 | O | [XX]() | [X]XX | XX | [Python]() |
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| 302 | O | [XX]() | [X]XX | XX | [Python]() |
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| 303 | O | [XX]() | [X]XX | XX | [Python]() |
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| 304 | O | [XX]() | [X]XX | XX | [Python]() |
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| 305 | O | [XX]() | [X]XX | XX | [Python]() |
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| 306 | O | [XX]() | [X]XX | XX | [Python]() |
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| 307 | O | [XX]() | [X]XX | XX | [Python]() |
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| 308 | O | [XX]() | [X]XX | XX | [Python]() |
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| 301 | O | [224. Basic Calculator](https://leetcode.com/problems/basic-calculator/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/224-basic-calculator.py) |
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| 302 | O | [227. Basic Calculator II](https://leetcode.com/problems/basic-calculator-ii/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/227-basic-calculator-ii.py) |
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| 303 | | [772. Basic Calculator III](https://leetcode.com/problems/basic-calculator-iii/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/772-basic-calculator-iii.py) |
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| 304 | O | [735. Asteroid Collision](https://leetcode.com/problems/asteroid-collision/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/735-asteroid-collision.py) |
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| 305 | O | [394. Decode String](https://leetcode.com/problems/decode-string/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/394-decode-string.py) |
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| 306 | | [1209. Remove All Adjacent Duplicates in String II](https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/1209-remove-all-adjacent-duplicates-in-string-ii.py) |
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| 307 | | [726. Number of Atoms](https://leetcode.com/problems/number-of-atoms/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/726-number-of-atoms.py) |
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| 308 | | [71. Simplify Path](https://leetcode.com/problems/simplify-path/) | [I]stack-queue | use stack to store the last states | [Python]([I]stack-queue/[I]stack-queue/71-simplify-path.py) |
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| 309 | O | [XX]() | [X]XX | XX | [Python]() |
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| 310 | O | [XX]() | [X]XX | XX | [Python]() |
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| 311 | O | [XX]() | [X]XX | XX | [Python]() |

‎[H]array/array.md

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@@ -511,3 +511,4 @@ two pointers opposite direction
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- like median
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- **use merge sort**
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- involve divide and conquer’s idea
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- during merging, we can utilize the relationship between left part elements and right part elements

‎[I]stack-queue/[I]stack-queue/1209-remove-all-adjacent-duplicates-in-string-ii.py

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class Solution:
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def removeDuplicates(self, s: str, k: int) -> str:
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stack = []
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for c in s:
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if not stack or stack[- 1][0] != c:
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stack.append([c, 1])
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else:
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stack[- 1][1] += 1
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if stack[- 1][1] == k:
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stack.pop()
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res = ''
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while stack:
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c, f = stack.pop()
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res = c * f + res
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return res
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# time O(n), n is the string's length
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# space O(n), due to stack
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# using stack and queue and use stack to store the last states

‎[I]stack-queue/[I]stack-queue/150-evaluate-reverse-polish-notation.py

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@@ -1,22 +1,22 @@
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class Solution:
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def evalRPN(self, tokens: List[str]) -> int:
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stack = []
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num_stack = []
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cal_stack = []
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for t in tokens:
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if t in '+-*/':
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second_num = stack.pop()
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first_num = stack.pop()
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num2 = num_stack.pop()
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num1 = num_stack.pop()
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if t == '+':
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stack.append(first_num + second_num)
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num_stack.append(num1 + num2)
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elif t == '-':
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stack.append(first_num - second_num)
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num_stack.append(num1 - num2)
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elif t == '*':
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stack.append(first_num * second_num)
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num_stack.append(num1 * num2)
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else:
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stack.append(int(first_num / second_num))
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num_stack.append(int(num1 / num2))
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else:
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stack.append(int(t))
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return stack[- 1]
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num_stack.append(int(t))
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return num_stack[- 1]
2020

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# time O(n), due to traverse
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# space O(n), due to stack

‎[I]stack-queue/[I]stack-queue/20-valid-parentheses.py

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@@ -1,17 +1,16 @@
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class Solution:
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def isValid(self, s: str) -> bool:
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stack = []
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close_open = {')': '(', '}': '{', ']': '['}
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stack = []
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for c in s:
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if c not in close_open:
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stack.append(c)
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else:
9-
if stack and close_open[c] == stack[- 1]:
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stack.pop()
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else:
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if not stack or stack[- 1] != close_open[c]:
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return False
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return len(stack) == 0
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stack.pop()
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return not stack
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# time O(n)
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# space O(n)
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# using stack and queue and use stack to store the last states and stack to check (LIFO) and hashmap
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# using stack and queue and use stack to store the last states and hashmap

‎[I]stack-queue/[I]stack-queue/224-basic-calculator.py

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class Solution:
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def calculate(self, s: str) -> int:
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s = '(' + s + ')'
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s = s.replace(' ', '')
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s = s.replace('(-', '(0-')
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num_stack = []
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cal_stack = []
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10+
def calc():
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num2 = num_stack.pop()
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num1 = num_stack.pop()
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cal = cal_stack.pop()
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if cal == '+':
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num_stack.append(num1 + num2)
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else:
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num_stack.append(num1 - num2)
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num = ''
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for i in range(len(s)):
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if s[i] == '(':
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cal_stack.append(s[i])
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elif s[i] == ')':
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while cal_stack and cal_stack[- 1] != '(':
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calc()
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cal_stack.pop()
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elif s[i] in '+-':
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while cal_stack and cal_stack[- 1] != '(':
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calc()
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cal_stack.append(s[i])
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else:
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num += s[i]
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if not s[i + 1].isdigit():
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num_stack.append(int(num))
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num = ''
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return num_stack[- 1]
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# time O(n)
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# space O(n)
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# using stack and queue and use stack to store the last states

‎[I]stack-queue/[I]stack-queue/227-basic-calculator-ii.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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num_stack = []
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cal_stack = []
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8+
def calc():
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num2 = num_stack.pop()
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num1 = num_stack.pop()
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cal = cal_stack.pop()
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if cal == '+':
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num_stack.append(num1 + num2)
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elif cal == '-':
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num_stack.append(num1 - num2)
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elif cal == '*':
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num_stack.append(num1 * num2)
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else:
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num_stack.append(int(num1 / num2))
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cal_weight = {'+': 0, '-': 0, '*': 1, '/': 1}
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num = ''
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for i in range(len(s)):
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if s[i] in '+-*/':
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while cal_stack and cal_weight[cal_stack[- 1]] >= cal_weight[s[i]]:
26+
calc()
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cal_stack.append(s[i])
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else:
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num += s[i]
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if i == len(s) - 1 or (i + 1 < len(s) and not s[i + 1].isdigit()):
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num_stack.append(int(num))
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num = ''
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34+
while cal_stack:
35+
calc()
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return num_stack[- 1]
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# time O(n)
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# space O(n)
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# using stack and queue and use stack to store the last states

‎[I]stack-queue/[I]stack-queue/346-moving-average-from-data-stream.py

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@@ -2,9 +2,9 @@
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class MovingAverage:
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def __init__(self, size: int):
5+
self.queue = deque([])
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self.size = size
67
self.total = 0
7-
self.queue = deque([])
88

99
def next(self, val: int) -> float:
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if len(self.queue) == self.size:
@@ -19,4 +19,4 @@ def next(self, val: int) -> float:
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2020
# time O(1)
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# space O(n)
22-
# using stacka and queue and use queue to simulate
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# using stack and queue and use queue to simulate

‎[I]stack-queue/[I]stack-queue/394-decode-string.py

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class Solution:
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def decodeString(self, s: str) -> str:
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stack = []
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cur = ''
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num = ''
7+
for i in range(len(s)):
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if s[i] == '[':
9+
stack.append((int(num), cur))
10+
num = ''
11+
cur = ''
12+
elif s[i] == ']':
13+
mul, prev = stack.pop()
14+
cur = prev + mul * cur
15+
elif s[i].isdigit():
16+
num += s[i]
17+
else:
18+
cur += s[i]
19+
return cur
20+
21+
# time O(n), not precisely (only true if max freq is small)
22+
# space O(n), not precisely (only true if max freq is small)
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# using stack and queue and use stack to store the last states

‎[I]stack-queue/[I]stack-queue/71-simplify-path.py

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class Solution:
2+
def simplifyPath(self, path: str) -> str:
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4+
stack = []
5+
path = path.split('/')[1:]
6+
7+
for c in path:
8+
if not c or c == '.':
9+
continue
10+
elif c == '..':
11+
if stack:
12+
stack.pop()
13+
else:
14+
stack.append(c)
15+
16+
return '/' + '/'.join(stack)
17+
18+
# time O(n), due to traverse and split
19+
# space O(n), due to stack and split
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# using stack and queue and use stack to store the last states

‎[I]stack-queue/[I]stack-queue/726-number-of-atoms.py

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from collections import defaultdict
2+
import string
3+
class Solution:
4+
def countOfAtoms(self, formula: str) -> str:
5+
element_freq = defaultdict(int)
6+
mul_stack = []
7+
num = ''
8+
element = ''
9+
mul = 1
10+
for i in range(len(formula) - 1, - 1, - 1):
11+
c = formula[i]
12+
if c == ')':
13+
mul *= int(num) if num else 1
14+
mul_stack.append(int(num) if num else 1)
15+
num = ''
16+
elif c == '(':
17+
mul //= mul_stack.pop()
18+
elif c.isdigit():
19+
num = c + num
20+
else:
21+
element = c + element
22+
if c in string.ascii_uppercase:
23+
element_freq[element] += mul * (int(num) if num else 1)
24+
element = ''
25+
num = ''
26+
27+
res = ''
28+
for e, f in sorted(element_freq.items()):
29+
res += e + (str(f) if f != 1 else '')
30+
return res
31+
32+
# time O(nlogn)
33+
# space O(n), due to stack and hashmap
34+
# using stack and queue and use stack to store the last states and hashmap and sort

‎[I]stack-queue/[I]stack-queue/735-asteroid-collision.py

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class Solution:
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def asteroidCollision(self, asteroids: List[int]) -> List[int]:
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stack = []
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5+
for weight in asteroids:
6+
if not stack:
7+
stack.append(weight)
8+
elif stack[- 1] < 0:
9+
stack.append(weight)
10+
elif stack[- 1] > 0 and weight > 0:
11+
stack.append(weight)
12+
else:
13+
while stack and stack[- 1] > 0 and weight < 0:
14+
if stack[- 1] > abs(weight):
15+
weight = 0
16+
break
17+
elif stack[- 1] == abs(weight):
18+
weight = 0
19+
stack.pop()
20+
break
21+
else:
22+
stack.pop()
23+
if weight:
24+
stack.append(weight)
25+
return stack
26+
27+
# time O(n), each asteroid push and pop at most once
28+
# space O(n), due to stack
29+
# using stack and queue and use stack to store the last states

‎[I]stack-queue/[I]stack-queue/772-basic-calculator-iii.py

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class Solution:
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def calculate(self, s: str) -> int:
3+
s = '(' + s + ')'
4+
5+
num_stack = []
6+
cal_stack = []
7+
8+
def calc():
9+
num2 = num_stack.pop()
10+
num1 = num_stack.pop()
11+
cal = cal_stack.pop()
12+
if cal == '+':
13+
num_stack.append(num1 + num2)
14+
elif cal == '-':
15+
num_stack.append(num1 - num2)
16+
elif cal == '*':
17+
num_stack.append(num1 * num2)
18+
else:
19+
num_stack.append(int(num1 / num2))
20+
21+
cal_weight = {'+': 0, '-': 0, '*': 1, '/': 1}
22+
num = ''
23+
for i in range(len(s)):
24+
if s[i] == '(':
25+
cal_stack.append(s[i])
26+
elif s[i] == ')':
27+
while cal_stack and cal_stack[- 1] != '(':
28+
calc()
29+
cal_stack.pop()
30+
elif s[i] in '+-*/':
31+
while cal_stack and cal_stack[- 1] != '(' and cal_weight[cal_stack[- 1]] >= cal_weight[s[i]]:
32+
calc()
33+
cal_stack.append(s[i])
34+
else:
35+
num += s[i]
36+
if not s[i + 1].isdigit():
37+
num_stack.append(int(num))
38+
num = ''
39+
return num_stack[- 1]
40+
41+
# time O(n)
42+
# space O(n)
43+
# using stack and queue and use stack to store the last states

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