/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var rob = function(root) {
    // Dynamic Programming approach
    const robSubTree = (root, map) => {
        if (!root) return 0;
        if (map.has(root)) return map.get(root);
        
        let money = 0;
        // rob grandchildren of root
        if (root.left) {
            money += robSubTree(root.left.left, map) + robSubTree(root.left.right, map);
        }
        if (root.right) {
            money += robSubTree(root.right.left, map) + robSubTree(root.right.right, map);
        }
        
        money = Math.max(money + root.val, robSubTree(root.left, map) + robSubTree(root.right, map));
        // memoizing to avoid repeated computation
        map.set(root, money);
        
        return money;
    }
    
    return robSubTree(root, new Map());
};