JavaScript Program to Check if an Array Contains only Unique Values

In this article, we are given an array, Our task is to find whether the elements in an array are unique or not.

Examples:

Input 1: 7,8,1,5,9                                                                                                                                                                                  
Output: true                                                                                                                                                                               
Input2: 7,8,1,5,5                                                                                                                                                                    
Output: false

In Input 1, elements 7,8,1,5,9 are distinct from each other and they were unique, there was no repetition of elements hence the array contains unique values. So the output is true, else the output is false.

Using of JavaScript Set

The set data structure is used to store the unique elements, it won't store the repeated or duplicate elements. If the size of the newly created set is equal to the size of the array, then the array contains unique elements. If not, it means the array contains duplicate or repeated elements.

Example: This example shows the use of the above-explained approach.

// JavaScript Approach using Set

function checkDistinct(array) {
    const checkSet = new Set(array);
    
    // Strict equality 
    // Return boolean value
    return checkSet.size === array.length;  
}

// Input 1
const input1 = [7, 8, 1, 5, 9];
console.log(checkDistinct(input1));

// Input 2
const input2 = [7, 8, 1, 5, 5];
console.log(checkDistinct(input2));

true
false

Time Complexity: O(N), N is the no of elements in the given array.

Auxiliary Space: O(N) , because of creating a Set Data Structure.

Using of indexOf() Method

This method is used to find the index of the first occurrence of the element. If the elements in the array are distinct, then the value returned by the indexOf() method is equal to the index of the element in the array. If repeated elements are present in the array, then the indexOf() method will return the first occurrence of the repeated element, hence the returned value and index of the element will differ.

Example: This example shows the use of the above-explained approach.

//JavaScript Program using indexOf() method

function checkDistinct(array) {
    for (let i = 0; i < array.length; i++) {
        if (array.indexOf(array[i]) !== i) {
            return false;
        }
    }
    return true;
}

// Input1
const input1 = [7, 8, 1, 5, 9];
console.log(checkDistinct(input1));

//Input2
const input2 = [7, 8, 1, 5, 5];
console.log(checkDistinct(input2));

true
false

Time Complexities: O(n^2), where N is the size of the array.

Auxiliary space: O(1), no space required.

Using Array.filter() and Array.includes()

Using `Array.filter()` with a callback that checks if an element's index is equal to its first occurrence's index in the array (`Array.indexOf()`), the function filters out duplicate elements. The resulting array's length equals the original if it contains only unique values.

Example:

function hasUniqueValues(arr) {
    return arr.filter((value, index, self) => self.indexOf(value) === index).length === arr.length;
}


console.log(hasUniqueValues([1, 2, 3, 4, 5])); // true
console.log(hasUniqueValues([1, 2, 2, 3, 4])); // false

true
false

Using Array.sort() and Array.every()

This approach involves sorting the array first and then checking if any consecutive elements are the same using Array.every().

Example: This example shows the use of the above-explained approach.

function checkDistinct(array) {
    array.sort((a, b) => a - b);
    return array.every((value, index) => index === 0 || value !== array[index - 1]);
}

// Input 1
const input1 = [7, 8, 1, 5, 9];
console.log(checkDistinct(input1));

// Input 2
const input2 = [7, 8, 1, 5, 5];
console.log(checkDistinct(input2));
// Nikunj Sonigara

true
false

Using an object to track seen values

Using an object to track seen values involves iterating through the array and storing each value as a key in the object. If a value already exists as a key, it indicates a duplicate. This method is efficient for checking uniqueness in arrays.

Example

function hasUniqueValues(arr) {
    let seen = {};
    for (let val of arr) {
        if (seen[val]) {
            return false;
        }
        seen[val] = true;
    }
    return true;
}

console.log(hasUniqueValues([1, 2, 3, 4]));
console.log(hasUniqueValues([1, 2, 2, 4])); 

true
false