Check whether array A is a permutation.

Task description

A non-empty zero-indexed 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.

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

Write a function:

int solution(int A[], int N);

that, given a zero-indexed 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.

Assume that:

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].

Complexity:

expected worst-case time complexity is O(N);

expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).

Elements of input arrays can be modified.

Copyright 2009�C2014 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.

Solution  C:42

 

 

#define FLAG(N) (((N)>>30)&0x3)
#define VALUE(N)  ((N)&(0xffffffff>>2))
#define SET_FLAG(N, flag) ((N)|((flag)<<30))
#define NOT_VISITED 0
#define VISITED 1
 
int solution(int A[], int N)
{
    int notFound = N;
    char* reason = "good";
    int  i = 0;
    for( i = 0; i < N; i++ )
    {
        int value = VALUE(A[i]);
        if(value > N)
        {
            // 数字超过N,不可能是全排列
            reason = "overflow";
            break;
        }
        int next = value - 1;
        if( FLAG(A[next]) == NOT_VISITED )
        {
            A[next] = SET_FLAG( A[next], VISITED);
            notFound --;
        }
        else
        {
            // 出现重复的元素, 不可能是全排列
            reason = "duplicate";
            break;
        }
    }
    //printf("reason:%s", reason);
    return (notFound == 0);
}

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