Swust OJ 2516 coach I want to learn arithmetic dp+ combination count

#include <stdio.h> #include <string.h> #include <iostream> #include <string> #include <queue > #include <cmath> #include <map> #include <algorithm> #include <vector>//#define Debugusing namespace Std;const int inf = 0x3fffffff;const int mod = 1000000007;const int mmax = 1000010;typedef long Long ll;int n,m K LL Inv[mmax]; LL Jie[mmax];    LL dp[1100];void Pre () {inv[0]=inv[1]=1;    Jie[0]=jie[1]=1;        for (int i=2;i<mmax;i++) {inv[i]= (LL) (mod-mod/i) *inv[mod%i]%mod;        Jie[i]=jie[i-1]*i;    Jie[i]%=mod;        } for (int i=2;i<mmax;i++) {inv[i]*=inv[i-1];    Inv[i]%=mod;    }}ll Pow_mod (ll x, int n) {ll res=1,tmp=x;        for (; n;n/=2) {if (n&1) res= (res*tmp)%mod;    tmp= (tmp*tmp)%mod; } return res;    LL C (int x,int y) {if (y>x) return 0; return jie[x]*inv[y]%mod*inv[x-y]%mod;}    void Build () {dp[0]=0;    Dp[1]=1; for (int i=2;i<=n;i++) {Dp[i]=pow_mod (I,n);            for (int j=1;j<i;j++) {dp[i]-=dp[i-j]*c (i,j)%mod;        dp[i]= (dp[i]%mod+mod)%mod;    }}}int Main () {pre ();            while (~SCANF ("%d%d%d", &n,&m,&k)) {if (m==1) {printf ("%lld\n", Pow_mod (K,n));        Continue        } build ();        LL cnt=0;                for (int i=0;i<=n;i++) {for (int j=0;i+j<=n;j++) {LL tmp=1;                Tmp=c (k,i) *c (k-i,j)%mod*c (k-i-j,j)%mod;                Tmp*=dp[i+j]*dp[i+j]%mod*pow_mod (LL) i,n* (m-2))%mod;                Tmp%=mod;                cnt+=tmp;            Cnt%=mod;    }} printf ("%lld\n", CNT); } return 0;}

Swust OJ 2516 coach I want to learn arithmetic dp+ combination count