find_the_second_largest_number_in_an_array.md

Find the Second Largest Number in an Array

Find the Second Largest Number in an Array

To find the second largest number in an array, iterate through the array and keep track of the largest and second largest elements.

Algorithm:

1. Initialize two variables, first and second, to -Infinity.
2. Iterate through the array, and for each element, check if it is greater than first.
3. If it is, update second to first and then update first to the current element.
4. If the element is smaller than first but greater than second, update second.
5. Return second as the second largest element.

Example:

function findSecondLargest(arr) {
    let first = -Infinity, second = -Infinity;
    for (let num of arr) {
        if (num > first) {
            second = first;
            first = num;
        } else if (num > second && num !== first) {
            second = num;
        }
    }
    return second;
}

// Example usage
console.log(findSecondLargest([10, 20, 4, 45, 99])); // Output: 45
console.log(findSecondLargest([1, 1, 1])); // Output: -Infinity

This method has a time complexity of O(n), where n is the length of the array.

Tags: basic, JavaScript, Arrays, Algorithm