May 14Easy

Check if array is good

Array
Hash Table
Sorting

Problem

You are given an integer array nums. We consider an array good if it is a permutation of an array base[n]. base[n] = [1, 2, ..., n - 1, n, n] (in other words, it is an array of length n + 1 which contains 1 to n - 1 exactly once, plus two occurrences of n). For example, base[1] = [1, 1] and base[3] = [1, 2, 3, 3].

Return true if the given array is good, otherwise return false. Note: A permutation of integers represents an arrangement of these numbers.

Solution

class Solution:
    def isGood(self, nums: List[int]) -> bool:
        set_nums = set(range(1, len(nums)))
        seen = False
        for num in nums:
            if num not in set_nums:
                if num == len(nums) - 1:
                    if seen:
                        return False
                    seen = True
                else:
                    return False
            else:
                set_nums.remove(num)
        return seen