Codeforces #260(Div 2) D A lot of games(字母树+树形dp)

解题思路：

  构建字母树，通过dfs判断每一局的输赢，再根据K进行分类讨论。

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#define LL long long
using namespace std;
const int maxn = 100000 + 10;
string s;
int G[maxn][30];
int win[maxn] , lose[maxn];
int n , k, cur;
void insert(string str)
{
	int len = str.length();
	int root = 0;
	for(int i=0;i<len;i++)
	{
		int x = s[i] - 'a';
		if(!G[root][x]) G[root][x] = ++cur;
		root = G[root][x];
	}
}
void dfs(int u)
{
	int ok = 0;
	for(int i=0;i<=26;i++)
	{
		if(G[u][i])
		{
			dfs(G[u][i]);
			ok = 1;
			win[u] |= !win[G[u][i]];
			lose[u] |= !lose[G[u][i]];
		}
	}
	if(!ok) lose[u] = 1;
}
int main()
{
	while(scanf("%d%d",&n,&k)!=EOF)
	{
		cur = 0;
		for(int i=1;i<=n;i++)
		{
			cin>>s;
			insert(s);
		}
		dfs(0);
		if(k == 1) win[0] ? printf("First\n") : printf("Second\n");
		else if(win[0] && lose[0])
		{
			printf("First\n");
		}
		else if(win[0])
		{
			(k & 1) ? printf("First\n") : printf("Second\n");
		}
		else printf("Second\n");
	}
	return 0;
}