Wannafly模拟赛 树（dp）

题目：https://www.nowcoder.com/acm/contest/submit/86fc8c46a8ce4c1fba763b8cf311f805?ACMContestId=2&tagId=4
思路：当时瞎想，题目说了是一棵树，其实不用管连接了，直接dp就行了
用dp[i][j]代表i个结点用j种颜色合法的方案数
dp[i][j] = dp[i-1][j] + dp[i-1][j-1] * (k - (j-1))
代码：

#include<bits/stdc++.h>using namespace std;typedef long long ll;const int MOD = 1e9+7;const int N = 305;ll dp[N][N];int main(){    int n,k;    scanf("%d %d",&n,&k);    int u,v;    for(int i = 1;i <= n-1;i++)        scanf("%d %d",&u,&v);    dp[0][0] = 1;    for(int i = 1;i <= n;i++)        for(int j = 1;j <= k;j++)            dp[i][j] = (dp[i-1][j] + dp[i-1][j-1] * (k - (j-1))) % MOD;    ll ans = 0;    for(int i = 1;i <= k;i++)        ans = (ans + dp[n][i]) % MOD;    printf("%lld\n",ans);    return 0;}//dp[i][j] = dp[i-1][j] + dp[i-1][j-1] * (k - (j-1))