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[Algorithm] PermCheck


Question

A non-empty array A consisting of N integers is given.

A permutation is a sequence containing each element from 1 to N once, and only once.

For example, array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3
    A[3] = 2

is a permutation, but array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3

is not a permutation, because value 2 is missing.

The goal is to check whether array A is a permutation.

Write a function:

function solution(A);

that, given an array A, returns 1 if array A is a permutation and 0 if it is not.

For example, given array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3
    A[3] = 2

the function should return 1.

Given array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3

the function should return 0.

Write an efficient algorithm for the following assumptions:

  • N is an integer within the range [1..100,000];
  • each element of array A is an integer within the range [1..1,000,000,000].

Solution (TypeScript)

function solution(a: number[]) {
  const array = [];
  const length = a.length;
  for (let i = 0; i < length; i += 1) {
    const val = a[i];
    if (array[val - 1] || val > length) {
      return 0;
    }
    array[val - 1] = val;
  }
  return 1;
}

Author: Codility, Lesson 4

20200107 Charyum.Park