Here is the problem's link : http://codeforces.net/contest/877/problem/D

In this problem I used BFS to solve it. In my WA submission I choose to break when the distance from the origin of the cell I am traversing is smaller or equal to the distance of the point of the front of the queue plus 1. In my accepted solution I choose to break when the distance from the origin of the cell I am traversing is smaller or equal to the distance of the point of the front of the queue. But I can't understand why my first solution fail. Can anyone give me the explanation ?

Correct : http://codeforces.net/contest/877/submission/31687084 WA: http://codeforces.net/contest/877/submission/31686998

The value of a node is the product of all the node in its subtree. So how do you update all the parent node when you update the child node ? The original problem is http://codeforces.net/gym/101466/problem/K.