[Usaco2010 Nov]Visiting Cows 拜访奶牛
时间限制:3s 空间限制:64MB
题目描述
经过了几周的辛苦工作,贝茜终于迎来了一个假期.作为奶牛群中最会社交的牛,她希望去拜访N(1<=n<=50000)个朋友.这些朋友被标号为1..n.这些奶牛有一个不同寻常的交通系统,里面有n-1条路,每条路连接了一对编号为c1和c2的奶牛(1 1="" <="C1" c1<="">C2).这样,在每一对奶牛之间都有一条唯一的通路. FJ希望贝茜尽快的回到农场.于是,他就指示贝茜,如果对于一条路直接相连的两个奶牛,贝茜只能拜访其中的一个.当然,贝茜希望她的假期越长越好,所以她想知道她可以拜访的奶牛的最大数目. =n<=50000)个朋友.这些朋友被标号为1..n.这些奶牛有一个不同寻常的交通系统,里面有n-1条路,每条路连接了一对编号为c1和c2的奶牛(1>
输入格式
第1行:单独的一个整数N 第2..N行:每一行两个整数,代表了一条路的C1和C2.
输出格式
单独的一个整数,代表了贝茜可以拜访的奶牛的最大数目.
样例输入
7 6 2 3 4 2 3 1 2 7 6 5 6 INPUT DETAILS: Bessie knows 7 cows. Cows 6 and 2 are directly connected by a road, as are cows 3 and 4, cows 2 and 3, etc. The illustration below depicts the roads that connect the cows: 1--2--3--4 | 5--6--7
样例输出
4 OUTPUT DETAILS: Bessie can visit four cows. The best combinations include two cows on the top row and two on the bottom. She can't visit cow 6 since that would preclude visiting cows 5 and 7; thus she visits 5 and 7. She can also visit two cows on the top row: {1,3}, {1,4}, or {2,4}.
提示
没有写明提示
题目来源
Gold