<jupyter_start><jupyter_text><jupyter_code># O(N) or O(N * log(N))
def solution(A):
    a = len(A)+1
    return  int(a * (a+1)/ 2 - sum(A))
solution([2,3,1,5])<jupyter_output><empty_output>
{'fraction_non_alphanumeric': 0.2222222222222222, 'fraction_numerical': 0.037037037037037035, 'mean_word_length': 5.333333333333333, 'pattern_counts': {'":': 0, '<': 5, '<?xml version=': 0, '>': 5, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
{'chain_length': '1', 'dir': 'jupyter-structured-clean-dedup', 'id': '343372', 'license': 'MIT', 'n_tokens_mistral': 96, 'n_tokens_neox': 93, 'n_words': 15, 'path': 'fun_coding/codility/3_PermMissingElem(Time_Complexity).ipynb', 'repo_name': 'kangyeolyoun2/python-coding-practice-folder', 'size': '189'}