Submission #1228473

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,int> plli;
typedef pair<int,pii> pipii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n);i>=0;i--)
#define rrep2(i,a,b) for (int i=(a);i>b;i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(),(a).end()

const int mod = 1e9 + 7;
const ll INF = 1<<30;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
const double pi = 3.141592653589793;

int n,m;
ll dp[305][305][305];

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> n >> m;
    dp[0][1][1]=1;
    rep2(i,1,m+1)rep2(j,1,n+1)rep2(k,1,j+1){
        if (j!=n) dp[i][j+1][k]+=(dp[i-1][j][k]*(n-j))%mod;
        dp[i][j][k]+=(dp[i-1][j][k]*(j-k))%mod;
        dp[i][j][j]+=(dp[i-1][j][k]*k)%mod;
    }
    cout << dp[m][n][n]%mod << endl;
    return 0;
}

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