1615F - LEGOndary Grandmaster - CodeForces Solution

#include<iostream>
#include<string>
using namespace std;
const int maxn=2005,mod=1000000007;
int T,n;
int f[maxn][maxn+maxn],g[maxn][maxn+maxn];
string s,t;
int main(){
	cin>>T;
	while(T--){
		cin>>n;
		cin>>s>>t;
		for(int i=1;i<n;i+=2){
			s[i]^=1;
			t[i]^=1;
		}
		s=" "+s;
		t=" "+t;
		f[0][n]=1;
		for(int i=1;i<=n;i++)
			for(int j=n-i;j<=n+i;j++)
				for(int x=0;x<=1;x++)
					for(int y=0;y<=1;y++)
						if((x^1)!=s[i]-'0'&&(y^1)!=t[i]-'0'){
							f[i][j+x-y]=(f[i][j+x-y]+f[i-1][j])%mod;
							g[i][j+x-y]=((g[i][j+x-y]+g[i-1][j])%mod+1ll*abs(j-n)*f[i-1][j])%mod;
						}
		cout<<g[n][n]<<'\n';
		for(int i=0;i<=n;i++)
			for(int j=0;j<=n+n;j++)
				f[i][j]=g[i][j]=0;
	}
	return 0;
}