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

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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 longusing 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;}

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