"Bzoj 2060" [Usaco2010 nov]visiting cows visit cows

2060: [Usaco2010 nov]visiting cows visiting cows

Time Limit:3 Sec Memory limit:64 MB
submit:257 solved:190
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Description

After weeks of hard work, Bessie finally ushered in a holiday. As the most sociable cow in the herd, she wants to visit N (1<=n<=50000) friends. These friends were labeled 1. N. These cows have an unusual transport system with N-1 roads, each connecting a pair of cows numbered C1 and C2 (1 <= C1 <= N; 1 <= C2 <= N; C1<>C2). In this way, there is a unique pathway between each pair of cows. FJ hoped that Bessie would return to the farm as soon as possible. So he instructed Bessie to visit only one of the two cows that were directly connected to a road. Of course, Bessie wanted her vacation to be as long as possible, so she wanted to know the maximum number of cows she could visit.
Input

Line 1th: A single integer n 2nd. N rows: Two integers per line representing the C1 and C2 of a route.
Output

A single integer that represents the maximum number of cows that Bessie can visit.
Sample Input

7

6 2

3 4

2 3

1 2

7 6

3 p

INPUT DETAILS:

Bessie knows 7 cows. Cows 6 and 2 is directly connected by a road,

As is 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

Sample Output

4

OUTPUT DETAILS:

Bessie can visit four cows. The best combinations include the cows

On the top row and both on the bottom. She can ' t visit Cow 6 since

That would preclude visiting cows 5 and 7; Thus she visits 5 and

1. She can also visit-cows on the top row: {1,3}, {1,4}, or

{2,4}.

HINT

Source

Gold

Tree-shaped DP water problem.

< Span class= "Mrow" id= "mathjax-span-28109" >f [ i ] [ 0 Span style= "Display:inline-block; width:0px; Height:2.503em; " > Said i Not selected, to i Maximum answer for the subtree of the root;
< Span class= "Mrow" id= "mathjax-span-28124" >f [ i ] [ 1 Span style= "Display:inline-block; width:0px; Height:2.503em; " > Said i Not selected, to i The maximum answer for the root subtree.

F [I][0]=∑max (F [J ][0],F [J ][1])
F [I][1]=1+∑F [J ][0]

#include <iostream>#include <algorithm>#include <cmath>#include <cstdlib>#include <cstring>#include <cstdio>#define M 50005using namespace STD;structedge{intY,ne;} e[m*3];inttot,h[m],f[m][2],n;voidAddedge (intXintY) {e[++tot].y=y;    E[TOT].NE=H[X]; H[x]=tot;}voidDfsintXintFA) {f[x][1]=1, f[x][0]=0; for(intI=h[x];i;i=e[i].ne) {intY=E[I].Y;if(Y==FA)Continue;        DFS (Y,X); f[x][1]+=f[y][0],f[x][0]+=max (f[y][1],f[y][0]); }}intMain () {scanf("%d", &n); for(intI=1; i<n;i++) {intx, y;scanf("%d%d", &x,&y);        Addedge (x, y);    Addedge (Y,X); } DFS (1,0);printf("%d\n", Max (f[1][0],f[1][1]));return 0;}

"Bzoj 2060" [Usaco2010 nov]visiting cows visit cows