1448-Count-Good-Nodes-in-Binary-Tree.ts

function goodNodes(root: TreeNode | null): number {
    // edge case
    if (root === null) return 0;

    //keep track of the count
    let count = 0;

    const dfs = (root, max) => {
        //if value is bigger than max of path, then it is a good node
        if (root.val >= max) count++;

        //extend search to children if not null with updated max(takes current node in consideration too)
        if (root.left !== null) dfs(root.left, Math.max(max, root.val));
        if (root.right !== null) dfs(root.right, Math.max(max, root.val));
    };

    //starts with negative max value, because min value is just the smaller positive value in javascript
    dfs(root, -Number.MAX_VALUE);

    return count;
}