Given an integer array nums, return the largest perimeter of a triangle with a non-zero area, formed from three of these lengths. If it is impossible to form any triangle of a non-zero area, return 0.

largestPerimeter.js

/**
 * Finds the largest perimeter of a triangle that can be formed from the given array of side lengths.
 * A triangle is valid if the sum of any two sides is greater than the third side.
 *
 * @param {number[]} nums - Array of positive integers representing side lengths.
 * @return {number} - The largest perimeter of a valid triangle, or 0 if none can be formed.
 */
var largestPerimeter = function(nums) {
    // Sort the array in descending order to try the largest sides first
    nums.sort((a, b) => b - a);

    // We only need to check up to the third-to-last element
    const n = nums.length - 2;

    // Iterate through the sorted array to find the first valid triangle
    for (let i = 0; i < n; i++) {
        // Check if the current triplet can form a triangle
        // Triangle inequality: sum of two smaller sides > largest side
        if (nums[i] < nums[i + 1] + nums[i + 2]) {
            // If valid, return the perimeter
            return nums[i] + nums[i + 1] + nums[i + 2];
        }
    }

    // If no valid triangle is found, return 0
    return 0;
};