B"You are given a tree (a connected undirected graph without cycles) of n vertices. Each of the n - 1 edges of the tree is colored in either black or red. You are also given an integer k . Consider sequences of k vertices. Let's call a sequence [a_1, a_2, ldots, a_k] good if it satisfies the following criterion: Consider the tree on the picture. If k=3 then the following sequences are good: [1, 4, 7] , [5, 5, 3] and [2, 3, 7] . The following sequences are not good: [1, 4, 6] , [5, 5, 5] , [3, 7, 3] . There are n^k sequences of vertices, count how many of them are good. Since this number can be quite large, print it modulo 10^9+7 . The first line contains two integers n and k ( 2 <= n <= 10^5 , 2 <= k <= 100 ), the size of the tree and the length of the vertex sequence. Each of the next n - 1 lines contains three integers u_i , v_i and x_i ( 1 <= u_i, v_i <= n , x_i in {0, 1 } ), where u_i and v_i denote the endpoints of the corresponding edge and x_i is the color of this edge ( 0 denotes red edge and 1 denotes black edge). Print the number of good sequences modulo 10^9 + 7 . In the first example, all sequences ( 4^4 ) of length 4 except the following are good: In the second example, all edges are red, hence there aren't any good sequences. "...