문제출처

문제

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.

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) (not counting the storage required for input arguments).

풀이과정

작성코드

• Detected time complexity: O(N) or O(N * log(N))

function solution(A) {
    var len = A.length;
    var sum = (N * (N+1)) / 2;
    var cnt = [];
    for (var i in A) {
        sum -= A[i];
        if (tap[A[i]]) {
            return 0;
        }
        tap[A[i]] = true;
    }
    return +(sum==0);
}

작성코드 Final

• Detected time complexity: O(N) or O(N * log(N))

function solution(A) {
    var cnt = [];
    var len = A.length;
    for (var i=0; i<len;i++) {
        cnt[i] = 0;   
    }
    for (var i=0; i<len;i++) {
        if (A[i] == 0 || A[i] > len) 
            return 0;       
        cnt[A[i]-1]++;         
        if(cnt[A[i]-1] > 1) 
            return 0;
    }
    return 1;
}