poj 3342 树形dp

还是简单的树形dp，不过要判断最优解是否有多种。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <map>
using namespace std;

const int N = 201;
int head[N];
int dp[N][2];
bool flag[N][2];
int n, e, cnt;
map<string, int> mp;

struct Edge
{
    int v, next;
} edge[N];

void addEdge( int u, int v )
{
    edge[e].v = v;
    edge[e].next = head[u];
    head[u] = e++;
}

void dfs( int u )
{
    dp[u][0] = 0, dp[u][1] = 1;
    for ( int i = head[u]; i != -1; i = edge[i].next )
    {
        int v = edge[i].v;
        dfs(v);
        dp[u][1] += dp[v][0];
        if ( flag[v][0] )
        {
            flag[u][1] = true;
        }
        if ( dp[v][0] > dp[v][1] )
        {
            dp[u][0] += dp[v][0];
            if ( flag[v][0] )
            {
                flag[u][0] = true;
            }
        }
        else if ( dp[v][0] < dp[v][1] )
        {
            dp[u][0] += dp[v][1];
            if ( flag[v][1] )
            {
                flag[u][0] = true;
            }
        }
        else
        {
            dp[u][0] += dp[v][0];
            flag[u][0] = true;
        }
    }
}

char str1[N], str2[N];

int main ()
{
    while ( scanf("%d", &n), n )
    {
        e = 0;
        cnt = 1;
        memset( head, -1, sizeof(head) );
        mp.clear();
        scanf("%s", str1);
        mp[str1] = cnt++;
        for ( int i = 1; i < n; i++ )
        {
            scanf("%s%s", str1, str2);
            if ( mp.count(str1) == 0 )
            {
                mp[str1] = cnt++;
            }
            if ( mp.count(str2) == 0 )
            {
                mp[str2] = cnt++;
            }
            addEdge( mp[str2], mp[str1] );
        }
        memset( flag, false, sizeof(flag) );
        dfs(1);
        if ( dp[1][0] > dp[1][1] )
        {
            printf("%d", dp[1][0]);
            if ( !flag[1][0] )
                printf(" Yes
");
            else
                printf(" No
");
        }
        else if ( dp[1][1] > dp[1][0] )
        {
            printf("%d", dp[1][1]);
            if ( !flag[1][1] )
                printf(" Yes
");
            else
                printf(" No
");
        }
        else
        {
            printf("%d No
", dp[1][0]);
        }
    }
    return 0;
}