codeforces 522A A. Reposts(树形dp)

题目链接：

codeforces 522A

题目大意：

给出一个谣言传播的树，问最长的链。

题目分析：

水题，主要是利用map处理读入，建好树

dp转移方程很简单：

dp[u]=maxv∈Childrendp[v]+1dp[u] = \max_{v \in Children}dp[v]+1

AC代码：

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>
#include <map>
#include <cstring>
#include <cctype>
#include <vector>
#define MAX 207

using namespace std;

vector<int> e[MAX];
map<string,int> dic;
int dp[MAX];
int n,m,b;
const string joker = "polycarp";

void add ( int u , int v )
{
    e[u].push_back ( v );
    e[v].push_back ( u );
}

void handle ( string&s )
{
    int len = s.length();
    for ( int i = 0 ; i <len ; i++ )
        if ( isupper(s[i])) s[i] = (char)(s[i]+32);
}

void init ( )
{
    dic.clear();
    for ( int i = 0 ; i < MAX ; i++ )
        e[i].clear();
    n = 0;
}

void dfs ( int u , int p )
{
    dp[u] = 1;
    for ( int i =  0 ; i < e[u].size() ; i++ )
    {
        int v = e[u][i];
        if ( v == p ) continue;
        dfs ( v , u );
        dp[u] = max ( dp[u] , dp[v]+1 );
    }
}

int main ( )
{
    while ( ~scanf ( "%d" , &m ))
    {
        init ();
        string x,y,s;
        int u,v;
        while ( m-- )
        {
            cin >> x >> s >> y;
            handle( x );
            handle( y );
            if ( !dic[x] ) dic[x] = ++n;
            if ( !dic[y] ) dic[y] = ++n;
            add ( dic[x] , dic[y] );
        }
        b = dic[joker];
        dfs ( b , -1 );
        printf ( "%d\n" , dp[b] );
    }
}