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[USACO17DEC]Barn Painting G 题解
题面翻译 题意：给定一颗N个节点组成的树，3种颜色，其中K个节点已染色，要求任意两相邻节点颜色不同，求合法染色方案数。 题目描述 Farmer John has a large farm with \(N\) barns (\(1 \le N \le 10^5\)), some of which are already painted and some not yet painted. Farmer John wanLuoguP4271 [USACO18FEB]New Barns P 树的直径+LCT
结论：如果边权非负，则距离树上一个点最远的点一定是直径端点之一. 由此可得我们只需维护树的直径就行. 这种维护方法的局限性在于不可以有删边操作. 假如合并两个连通块 A,B, 直径端点分别为 $x_{0},x_{1},x_{2},x_{3}$，新树直径的端点一定是在 4 个点中的两个.POJ 2749 Building roads 【经典2-SAT+二分枚举】
传送门：POJ 2749 Building roads Time Limit: 2000MS Memory Limit: 65536K Problem Description Farmer John’s farm has N barns, and there are some cows that live in each barn. The cows like to drop around, so John wants to build some roads to connect tP4084 [USACO17DEC]Barn Painting
题意翻译 题意：给定一颗N个节点组成的树，3种颜色，其中K个节点已染色，要求任意两相邻节点颜色不同，求合法染色方案数。 翻译贡献者：Il_ItzABC_lI 题目描述 Farmer John has a large farm with NN barns (1 \le N \le 10^51≤N≤105), some of which are already painted and some not