{"id":935,"date":"2024-09-25T21:59:08","date_gmt":"2024-09-25T21:59:08","guid":{"rendered":"https:\/\/algocademy.com\/blog\/why-i-just-failed-an-easy-technical-interview-in-computer-science-and-what-i-learned-from-it\/"},"modified":"2026-10-15T10:34:50","modified_gmt":"2026-10-15T10:34:50","slug":"why-i-just-failed-an-easy-technical-interview-in-computer-science-and-what-i-learned-from-it","status":"publish","type":"post","link":"https:\/\/algocademy.com\/blog\/why-i-just-failed-an-easy-technical-interview-in-computer-science-and-what-i-learned-from-it\/","title":{"rendered":"Failed an Easy Technical Interview? Why It Happens and What to Fix"},"content":{"rendered":"

If you failed a technical interview that felt easy, the cause is usually not the algorithm. The usual causes are small and fixable: you solved a slightly different problem than the one asked, you stayed silent while thinking, you missed edge cases, you never ran your code against an example, or nerves made you drop things you know. This post helps you work out which one it was and what to practice before the next round.<\/p>\n

One note on honesty: this is a guide, not a personal story. The earlier version of this post was written as a first-person account; the advice below is general, and it is the order in which we would debrief a failed interview.<\/p>\n

Why “easy” problems fail people<\/h2>\n

Interviewers do not grade the problem only on whether you reach the answer. They look at how you get there. A problem that is easy for the interviewer to solve is a problem where there is nothing to hide behind, so small habits show up clearly. In rough order of how often they cause a rejection:<\/p>\n

    \n
  1. Starting to code before understanding the problem.<\/strong> You assumed the input was sorted, or non-empty, or only lowercase letters, and you never asked.<\/li>\n
  2. Silence.<\/strong> Even a correct solution can read as a weak signal if the interviewer cannot see how you think. They also cannot give you the small nudge they would otherwise give.<\/li>\n
  3. No testing.<\/strong> You said “done” without walking an example through the code, and a bug sat in plain sight.<\/li>\n
  4. Edge cases.<\/strong> Empty input, one element, duplicates, negative numbers, all elements equal.<\/li>\n
  5. Messy code.<\/strong> Unclear names, one giant function, copy-pasted branches.<\/li>\n
  6. Not recovering from a mistake.<\/strong> You noticed a bug, froze, and lost the next ten minutes.<\/li>\n
  7. Nerves.<\/strong> Anxiety narrows attention. It is why people blank on syntax they use every day.<\/li>\n<\/ol>\n

    An example: a small problem with many ways to slip<\/h2>\n

    The task: check whether a string is a palindrome, ignoring case and anything that is not a letter or digit.<\/em> This is a standard easy problem. Here is how a good attempt goes.<\/p>\n

    Clarify first.<\/strong> Is the empty string a palindrome? Is Unicode a concern, or only ASCII? Can I modify the input? (Strings are immutable in Python, so that one is moot, but in other languages it matters.) Two minutes of questions are worth more than any trick.<\/p>\n

    State a plan out loud.<\/strong> “I will use two pointers from both ends, skip characters that are not alphanumeric, and compare in lowercase. That is O(n) time and O(1) extra space. A simpler version would build a cleaned copy and compare it with its reverse, which uses O(n) extra space; I can start there if you prefer.”<\/p>\n

    def is_palindrome(s):\n    left, right = 0, len(s) - 1\n    while left < right:\n        while left < right and not s[left].isalnum():\n            left += 1\n        while left < right and not s[right].isalnum():\n            right -= 1\n        if s[left].lower() != s[right].lower():\n            return False\n        left += 1\n        right -= 1\n    return True\n\ntests = [\"A man, a plan, a canal: Panama\", \"race a car\", \"\", \" \", \".,\", \"a\", \"ab\"]\nfor t in tests:\n    print(repr(t), is_palindrome(t))<\/code><\/pre>\n
    Output:<\/p>\n
    'A man, a plan, a canal: Panama' True\n'race a car' False\n'' True\n' ' True\n'.,' True\n'a' True\n'ab' False<\/code><\/pre>\n
    Now the places where an “easy” attempt breaks:<\/p>\n