donnemartin/interactive-coding-challenges · error · Exception
Stack is full
Error message
Stack is full
What it means
n_stacks' push raises Exception('Stack is full') when the given stack's pointer has reached stack_size - 1, i.e. that virtual stack within the single backing array is at capacity. The implementation divides one array into N fixed-size stacks, so overflow of any one stack cannot be absorbed by neighbors.
Source
Thrown at stacks_queues/n_stacks/n_stacks_solution.ipynb:129
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [],
"source": [
"class Stacks(object):\n",
"\n",
" def __init__(self, num_stacks, stack_size):\n",
" self.num_stacks = num_stacks\n",
" self.stack_size = stack_size\n",
" self.stack_pointers = [-1] * self.num_stacks\n",
" self.stack_array = [None] * self.num_stacks * self.stack_size\n",
"\n",
" def abs_index(self, stack_index):\n",
" return stack_index * self.stack_size + self.stack_pointers[stack_index]\n",
"\n",
" def push(self, stack_index, data):\n",
" if self.stack_pointers[stack_index] == self.stack_size - 1:\n",
" raise Exception('Stack is full')\n",
" self.stack_pointers[stack_index] += 1\n",
" array_index = self.abs_index(stack_index)\n",
" self.stack_array[array_index] = data\n",
"\n",
" def pop(self, stack_index):\n",
" if self.stack_pointers[stack_index] == -1:\n",
" raise Exception('Stack is empty')\n",
" array_index = self.abs_index(stack_index)\n",
" data = self.stack_array[array_index]\n",
" self.stack_array[array_index] = None\n",
" self.stack_pointers[stack_index] -= 1\n",
" return data"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [View on GitHub (pinned to 358f2cc604)
Solutions
- Pop from the stack before pushing again, or check space with the pointer/stack_size before pushing
- Construct the stacks with a larger stack_size if more elements are needed
- Wrap push in try/except and grow/drop on overflow if using this class in real code
Example fix
# before
stacks.push(0, item) # may raise 'Stack is full'
# after
stack_size = stacks.stack_size
if stacks.stack_pointers[0] < stack_size - 1:
stacks.push(0, item)
else:
stacks.pop(0)
stacks.push(0, item) Defensive patterns
Strategy: validation
Validate before calling
if stacks.stack_pointers[stack_index] < stacks.stack_size - 1:
stacks.push(stack_index, data)
else:
raise_or_handle_full(stack_index) Try / catch
try:
stacks.push(i, item)
except Exception as e:
if str(e) == 'Stack is full':
stacks.pop(i) # make room or route elsewhere
else:
raise Prevention
- Size stack_size to the max expected per stack
- Track push counts per stack_index
- Pop before pushing in bounded buffers
When it happens
Trigger: Calling push(stack_index, data) more than stack_size times on the same stack_index; e.g. stack_size=5 and a sixth push to stack 0 raises. Also when defaulting stack_size too small for the workload.
Common situations: Fixed-capacity buffer sizing in interviews/exercises; forgetting that capacity is per virtual stack, not total; loops that push without tracking counts.
Related errors
AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28).
Data as JSON: /api/errors/2358da3179813384.
Report an issue: GitHub.