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[Algorithm] PermMissingElem


Question

An 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:

function solution(A);

that, given an 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.

Write an efficient algorithm for the following assumptions:

  • 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)].

Solution (TypeScript)

function solution(n: number[]) {
  const tmp = {};
  for (let i = 0; i < n.length; i += 1) {
    if (!tmp[i + 1]) {
      tmp[i + 1] = false;
    }
    tmp[n[i]] = true;
  }
  
  for (let key of Object.keys(tmp)) {
    if (!tmp[key]) {
      return parseInt(key);
    }
  }
  return n.length + 1;
}

Author: Codility, Lesson 3

20200104 Charyum.Park