Скачать или смотреть Codility - PermCheck (JavaScript) - Part 1/2

Lesson 4 -Counting Elements.

Part 1 of 2.
Part 2 link:    • Codility - PermCheck (JavaScript) - Part 2/2  
Task Description:
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:

class Solution { public int solution(int[] 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].