已知一颗有根树是 2

代码说明：

已知一颗有根树是 2-tree（只有度为2和度为0的结点），并且有n个叶子节点，从左到右编号为1,2,…, n，还知道两个相邻编号节点之间的 ChonSu（这棵树中这链接这两个节点的路径的边数）。求任意两个叶子节点x, y （1≤x≤n）之间的 ChonSu-Rooted tree is known to a 2-tree (only the degree 2 and degree 0 nodes), and there are n-leaf nodes from left to right numbered 1,2, ..., n, also know that two adjacent numbers between nodes ChonSu (this tree that links these two nodes in the path of the number of edges). Seeking any two leaf nodes x, y (1 ≤ x ≤ n) between the ChonSu