krahets/hello-algo · error · IndexError

キューがいっぱいです

Error message

キューがいっぱいです

What it means

This IndexError (Japanese: 'キューがいっぱいです' = 'queue is full') is raised by ArrayQueue.push(num) (array_queue.py:32) when the number of live elements equals the backing array length. ArrayQueue is a fixed-capacity circular-array queue — unlike the deque in this repo, the queue does NOT auto-grow, so pushing past capacity is a hard error. The capacity is the integer passed to the constructor `ArrayQueue(size)`.

Source

Thrown at ja/codes/python/chapter_stack_and_queue/array_queue.py:32

        self._front: int = 0  # 先頭ポインタ。先頭要素を指す
        self._size: int = 0  # キューの長さ

    def capacity(self) -> int:
        """キューの容量を取得"""
        return len(self._nums)

    def size(self) -> int:
        """キューの長さを取得"""
        return self._size

    def is_empty(self) -> bool:
        """キューが空かどうかを判定"""
        return self._size == 0

    def push(self, num: int):
        """エンキュー"""
        if self._size == self.capacity():
            raise IndexError("キューがいっぱいです")
        # 末尾ポインタを計算し、末尾インデックス + 1 を指す
        # 剰余演算により、rear が配列末尾を越えた後に先頭へ戻るようにする
        rear: int = (self._front + self._size) % self.capacity()
        # num をキュー末尾に追加
        self._nums[rear] = num
        self._size += 1

    def pop(self) -> int:
        """デキュー"""
        num: int = self.peek()
        # 先頭ポインタを1つ後ろへ進め、末尾を越えたら配列先頭に戻す
        self._front = (self._front + 1) % self.capacity()
        self._size -= 1
        return num

    def peek(self) -> int:
        """キュー先頭の要素にアクセス"""
        if self.is_empty():

View on GitHub (pinned to 69932aed18)

Solutions

1. Check `if queue.size() < queue.capacity(): queue.push(num)` before pushing.
2. Size the constructor capacity to the maximum concurrent elements: `ArrayQueue(max_concurrent)`.
3. In a producer/consumer pattern, pop() before push() when at capacity, or use a growable structure.
4. Wrap push in try/except IndexError if dropping on full is acceptable.

Example fix

// before
q = ArrayQueue(5)
for i in range(10):
    q.push(i)  # IndexError on the 6th push

// after
q = ArrayQueue(5)
for i in range(10):
    if q.size() == q.capacity():
        q.pop()
    q.push(i)

if queue.size() < queue.capacity():
    queue.push(num)
else:
    # at capacity: pop first, resize at construction, or drop
    pass

def queue_has_room(q: ArrayQueue) -> bool:
    return q.size() < q.capacity()

try:
    queue.push(num)
except IndexError:
    # queue full — enqueue failed; apply backpressure or drop
    pass

When it happens

Trigger: Calling push() after `self._size == self.capacity()`. Pushing more than the constructor-supplied size elements without an equal number of pop() calls. Using a small capacity (e.g. ArrayQueue(5)) and pushing 6 times.

Common situations: Underestimating the required capacity at construction time. Producer faster than consumer in a producer/consumer setup with no backpressure check. Confusing this fixed-capacity queue with Python's unbounded collections.deque. The driver loop at the bottom of the file pushes then pops each round to stay within capacity — omitting the pop triggers this.

Related errors

• 队列已满
• キューが空です
• 佇列已滿
• очередь заполнена
• 佇列已滿

AI-assisted analysis of krahets/hello-algo@69932aed18 (2026-08-13). Data as JSON: /api/errors/a25193b75bd74cae. Report an issue: GitHub.