Give me a few mins , i will update it with an example 
Aaah. That was harsh!
Thanks alot
Awesome explanation with the images, just give a link in official editorial as different approach to the problem
precisely , yes you are right . i mixed variable M with Q . thanks for the correction
p is parent of u . And discovering means if we have already visited the node or not . I meant that if we havent visited any node in the subtree of u , then u should remain in the vector and once all the subtree nodes are visited , we have to pop u .
thank you