function validate(root){ if(!root.length){ return false; } if(!root[0]){ return false; } let currentNode = 0; let left = 1; let right = 2; while(right <= root.length){ if(root[currentNode] > root[left] && root[currentNode] < root[right]){ currentNode++; left = left + 2; right = right + 2; } else { return false; } } return true; } validate([5,1,4,34,4,3,6]);