Fetch Second minimum element from an array without sorting JavaScript

We have an array of Numbers, and we are required to write a function that returns the second smallest value from the array.

For example ? if the array is ?

const arr = [67, 87, 56, 8, 56, 78, 54, 67, 98, 56, 54];

Then the output should be the following ?

54

because 54 is the smallest value after 8

Method 1: Using indexOf and splice

This approach finds the minimum element, removes it from a copy of the array, then finds the minimum of the remaining elements.

const arr = [67, 87, 56, 8, 56, 78, 54, 67, 98, 56, 54];

const minimumIndex = arr => {
    return arr.indexOf(Math.min(...arr));
};

const secondMinimum = arr => {
    const copy = arr.slice();
    copy.splice(minimumIndex(copy), 1);
    return copy[minimumIndex(copy)];
};

console.log(secondMinimum(arr));

54

Method 2: Using Two Variables (More Efficient)

A more efficient approach that finds both minimum and second minimum in a single pass through the array.

const arr = [67, 87, 56, 8, 56, 78, 54, 67, 98, 56, 54];

const findSecondMinimum = arr => {
    if (arr.length < 2) return undefined;
    
    let min = Infinity;
    let secondMin = Infinity;
    
    for (let num of arr) {
        if (num < min) {
            secondMin = min;
            min = num;
        } else if (num < secondMin && num !== min) {
            secondMin = num;
        }
    }
    
    return secondMin === Infinity ? undefined : secondMin;
};

console.log(findSecondMinimum(arr));

54

Method 3: Using Set and Sort

This method removes duplicates first, then sorts to find the second smallest unique value.

const arr = [67, 87, 56, 8, 56, 78, 54, 67, 98, 56, 54];

const secondMinimumUnique = arr => {
    const unique = [...new Set(arr)].sort((a, b) => a - b);
    return unique.length >= 2 ? unique[1] : undefined;
};

console.log(secondMinimumUnique(arr));

54

Comparison

Conclusion

The two-variable approach is most efficient with O(n) time complexity. Use the Set method if you need the second smallest unique value, ignoring duplicates.