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codility 3-1. PermMissingElem

03 May 2017 | 알고리즘 프로그래밍

문제출처

문제

A zero-indexed array A consisting of N different integers is given. The array contains integers in the range [1..(N + 1)], which means that exactly one element is missing.

Your goal is to find that missing element.

Write a function:

def solution(A)
that, given a zero-indexed array A, returns the value of the missing element.

For example, given array A such that:

  A[0] = 2
  A[1] = 3
  A[2] = 1
  A[3] = 5
the function should return 4, as it is the missing element.

Assume that:

N is an integer within the range [0..100,000];
the elements of A are all distinct;
each element of array A is an integer within the range [1..(N + 1)].
Complexity:

expected worst-case time complexity is O(N);
expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.

풀이코드

  • Detected time complexity: O(N) or O(N * log(N))
def solution(A):
    li = [0] * (len(A) + 1)
    for i in A:
        li[i-1] = 1  
    return li.index(0) + 1

다른사람 코드

  • 와! 이렇게 쉬운 방법이 있었다니..
def solution(A):
  return sum (range(len(A)+2)) - sum(A)

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