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217. Contains Duplicate

Description

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

 

Example 1:

Input: nums = [1,2,3,1]

Output: true

Explanation:

The element 1 occurs at the indices 0 and 3.

Example 2:

Input: nums = [1,2,3,4]

Output: false

Explanation:

All elements are distinct.

Example 3:

Input: nums = [1,1,1,3,3,4,3,2,4,2]

Output: true

 

Constraints:

  • 1 <= nums.length <= 105
  • -109 <= nums[i] <= 109

Solutions

Solution 1: Sorting

First, we sort the array nums.

Then, we traverse the array. If there are two adjacent elements that are the same, it means that there are duplicate elements in the array, and we directly return true.

Otherwise, when the traversal ends, we return false.

The time complexity is $O(n \times \log n)$, where $n$ is the length of the array nums.

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class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        return any(a == b for a, b in pairwise(sorted(nums)))

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class Solution {
    public boolean containsDuplicate(int[] nums) {
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 1; ++i) {
            if (nums[i] == nums[i + 1]) {
                return true;
            }
        }
        return false;
    }
}

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class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        for (int i = 0; i < nums.size() - 1; ++i) {
            if (nums[i] == nums[i + 1]) {
                return true;
            }
        }
        return false;
    }
};

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func containsDuplicate(nums []int) bool {
    sort.Ints(nums)
    for i, v := range nums[1:] {
        if v == nums[i] {
            return true
        }
    }
    return false
}

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function containsDuplicate(nums: number[]): boolean {
    nums.sort((a, b) => a - b);
    const n = nums.length;
    for (let i = 1; i < n; i++) {
        if (nums[i - 1] === nums[i]) {
            return true;
        }
    }
    return false;
}

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impl Solution {
    pub fn contains_duplicate(mut nums: Vec<i32>) -> bool {
        nums.sort();
        let n = nums.len();
        for i in 1..n {
            if nums[i - 1] == nums[i] {
                return true;
            }
        }
        false
    }
}

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/**
 * @param {number[]} nums
 * @return {boolean}
 */
var containsDuplicate = function (nums) {
    return new Set(nums).size !== nums.length;
};

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public class Solution {
    public bool ContainsDuplicate(int[] nums) {
        return nums.Distinct().Count() < nums.Length;
    }
}

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class Solution {
    /**
     * @param Integer[] $nums
     * @return Boolean
     */
    function containsDuplicate($nums) {
        $numsUnique = array_unique($nums);
        return count($nums) != count($numsUnique);
    }
}

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