0543-diameter-of-binary-tree.js

/**
 * https://leetcode.com/problems/diameter-of-binary-tree/
 * TIme O(N) | Space O(H)
 * @param {TreeNode} root
 * @return {number}
 */
var diameterOfBinaryTree = function(root, max = [0]) {
    diameterOfTree(root, max);

    return max[0];
};

const diameterOfTree = (root, max) => {
    const isBaseCase = root === null;
    if (isBaseCase) return 0;

    return dfs(root, max);
}

const dfs = (root, max) => {
    const left = diameterOfTree(root.left, max);
    const right = diameterOfTree(root.right, max);

    const diameter = left + right;
    max[0] = Math.max(max[0], diameter);

    const height = Math.max(left, right);

    return height + 1;
}