donnemartin/interactive-coding-challenges · error · ValueError

prices must have at least two values

Error message

prices must have at least two values

What it means

Raised by Solution.find_max_profit when the prices list has fewer than 2 entries; a single price gives no buy/sell pair, so max profit is undefined. It is a defensive ValueError guard at the top of the method. The algorithm then pops the first element as the initial min price and iterates the rest.

Solutions

1. Ensure the caller passes at least two prices before invoking find_max_profit.
2. If a 0 profit is the desired behavior for <2 prices, catch the ValueError or check len(prices) >= 2 first and short-circuit to 0.
3. Pass a copy (list(prices)) since the method pops from the input list.

Example fix

# before
profit = Solution().find_max_profit([7])  # ValueError

# after
prices = [7]
profit = Solution().find_max_profit(prices) if len(prices) >= 2 else 0

if not isinstance(prices, (list, tuple)) or len(prices) < 2:
    raise ValueError('need at least two prices')
profit = Solution().find_max_profit(list(prices))

def has_two_prices(p):
    return isinstance(p, list) and len(p) >= 2

try:
    profit = s.find_max_profit(prices)
except ValueError as e:
    profit = 0  # or log and skip

When it happens

Trigger: Calling find_max_profit with a list of length 0 or 1, e.g. find_max_profit([5]) or find_max_profit([]).

Common situations: Passing an empty dataset from a file/API feed, or a test case that assumed a single price should return 0. Also note the method mutates its input via prices.pop(0).

Related errors

• array must have 3 or more ints
• rows and cols cannot be negative
• num_pairs cannot be < 0
• rows and cols cannot be None
• sentence cannot be None

AI-assisted analysis of donnemartin/interactive-coding-challenges@358f2cc604 (2026-08-28). Data as JSON: /api/errors/8d92574c3469930d. Report an issue: GitHub.

Appendix: source

Thrown at online_judges/max_profit/max_profit_solution.ipynb:105

    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import sys\n",
    "\n",
    "\n",
    "class Solution(object):\n",
    "\n",
    "    def find_max_profit(self, prices):\n",
    "        if prices is None:\n",
    "            raise TypeError('prices cannot be None')\n",
    "        if len(prices) < 2:\n",
    "            raise ValueError('prices must have at least two values')\n",
    "        min_price = prices.pop(0)\n",
    "        max_profit = prices[0] - min_price\n",
    "        for price in prices:\n",
    "            profit = price - min_price\n",
    "            min_price = min(price, min_price)\n",
    "            max_profit = max(profit, max_profit)\n",
    "        return max_profit"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "code",

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