Submission #7092607

---

Source Code Expand

#include<bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define all(c) (c).begin(),(c).end()
#define pb push_back
#define dbg(...) do{cerr<<__LINE__<<": ";dbgprint(#__VA_ARGS__, __VA_ARGS__);}while(0);

using namespace std;

namespace std{template<class S,class T>struct hash<pair<S,T>>{size_t operator()(const pair<S,T>&p)const{return ((size_t)1e9+7)*hash<S>()(p.first)+hash<T>()(p.second);}};template<class T>struct hash<vector<T>>{size_t operator()(const vector<T> &v)const{size_t h=0;for(auto i : v)h=h*((size_t)1e9+7)+hash<T>()(i)+1;return h;}};}
template<class T>ostream& operator<<(ostream &os, const vector<T> &v){os<<"[ ";rep(i,v.size())os<<v[i]<<(i==v.size()-1?" ]":", ");return os;}template<class T>ostream& operator<<(ostream &os,const set<T> &v){os<<"{ "; for(const auto &i:v)os<<i<<", ";return os<<"}";}
template<class T,class U>ostream& operator<<(ostream &os,const map<T,U> &v){os<<"{";for(const auto &i:v)os<<" "<<i.first<<": "<<i.second<<",";return os<<"}";}template<class T,class U>ostream& operator<<(ostream &os,const pair<T,U> &p){return os<<"("<<p.first<<", "<<p.second<<")";}
void dbgprint(const string &fmt){cerr<<endl;}template<class H,class... T>void dbgprint(const string &fmt,const H &h,const T&... r){cerr<<fmt.substr(0,fmt.find(","))<<"= "<<h<<" ";dbgprint(fmt.substr(fmt.find(",")+1),r...);}
typedef long long ll;typedef vector<int> vi;typedef pair<int,int> pi;const int inf = (int)1e9;const double INF = 1e12, EPS = 1e-9;

const int mod = 1e9 + 7;
int dp[2][301][301];

int main(){
	cin.tie(0); cin.sync_with_stdio(0);
	int n, m;
	cin >> n >> m;
	dp[0][1][0] = 1;
	int next = 1, cur = 0;
	rep(i, m){
		memset(dp[next], 0, sizeof(dp[next]));
		rep(j, n + 1) rep(k, n + 1) if(dp[cur][j][k]){
			// back 0
			if(j + k <= n)
			(dp[next][j + k][0] += (ll)dp[cur][j][k] * j % mod) %= mod;
			// forward
			if(k + 1 <= n)
			(dp[next][j][k + 1] += (ll)dp[cur][j][k] * max(0, n - j - k) % mod) %= mod;
			// stay
			(dp[next][j    ][k] += (ll)dp[cur][j][k] * k % mod) %= mod;
		}
		swap(cur, next);
	}
	//dbg(dp[2][3][0]);
	
	cout << dp[cur][n][0] << endl;
	return 0;
}

Submission Info

Judge Result