krahets/hello-algo · error · IndexError
佇列已滿
Error message
佇列已滿
What it means
Raised by the push() method of a circular-array-based queue when the number of elements equals the allocated capacity. Unlike ArrayDeque (which silently prints and returns on overflow), ArrayQueue raises an IndexError to enforce a hard capacity limit. The capacity is fixed at construction time (len(self._nums)) and does not auto-expand.
Source
Thrown at zh-hant/codes/python/chapter_stack_and_queue/array_queue.py:32
self._front: int = 0 # 佇列首指標，指向佇列首元素
self._size: int = 0 # 佇列長度
def capacity(self) -> int:
"""獲取佇列的容量"""
return len(self._nums)
def size(self) -> int:
"""獲取佇列的長度"""
return self._size
def is_empty(self) -> bool:
"""判斷佇列是否為空"""
return self._size == 0
def push(self, num: int):
"""入列"""
if self._size == self.capacity():
raise IndexError("佇列已滿")
# 計算佇列尾指標，指向佇列尾索引 + 1
# 透過取餘操作實現 rear 越過陣列尾部後回到頭部
rear: int = (self._front + self._size) % self.capacity()
# 將 num 新增至佇列尾
self._nums[rear] = num
self._size += 1
def pop(self) -> int:
"""出列"""
num: int = self.peek()
# 佇列首指標向後移動一位，若越過尾部，則返回到陣列頭部
self._front = (self._front + 1) % self.capacity()
self._size -= 1
return num
def peek(self) -> int:
"""訪問佇列首元素"""
if self.is_empty():View on GitHub (pinned to 69932aed18)
Solutions
- Check queue.size() < queue.capacity() before calling push()
- Increase the capacity argument at construction time to match peak load
- Pop before pushing if you need a fixed-size circular buffer that drops old items
- Switch to collections.deque if unbounded growth is acceptable
Example fix
# before
queue = ArrayQueue(5)
for i in range(10):
queue.push(i) # crashes at i=5
# after
queue = ArrayQueue(10)
for i in range(10):
queue.push(i)
# or check before push:
if queue.size() < queue.capacity():
queue.push(i) Defensive patterns
Strategy: validation
Validate before calling
if queue.size() < queue.capacity():
queue.push(num)
else:
# either increase capacity or drop oldest item
queue.pop()
queue.push(num) Try / catch
try:
queue.push(num)
except IndexError:
print("queue full, dropping item") Prevention
- Choose a capacity at construction time that matches peak expected load
- Check size() < capacity() before push() in producer code
- This queue does NOT auto-grow; use collections.deque if unbounded capacity is needed
When it happens
Trigger: Pushing more items than the constructor-specified capacity without popping in between; enqueuing at a rate faster than dequeuing in a producer-consumer setup; using a small capacity (e.g., ArrayQueue(5)) and overfilling it.
Common situations: Burst traffic exceeding a fixed buffer size; choosing an undersized capacity for the workload; forgetting that this queue does not auto-grow unlike Python's collections.deque.
Related errors
AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13).
Data as JSON: /api/errors/dd76038769f29079.
Report an issue: GitHub.