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126 | #include<bits/stdc++.h>
using namespace std;
#define ll long long
const ll m = 1000000007;
ll facs[10009];
int n;
ll facmod(ll n) {
if(n == 0)
return 1;
for(ll i = n - 1; i >= 1; i--) {
n = (n*i)%m;
}
return n;
}
ll modinv(ll a) {
ll res = 1;
ll exp = m - 2;
while(exp > 0) {
if(exp % 2 == 1) {
res = (res*a)%m;
}
exp >>= 1;
a = (a*a)%m;
}
return res;
}
ll choose(ll n, ll k) {
ll a = facs[n];
ll b = (facs[k] * facs[n-k]) % m;
return (a * modinv(b))%m;
}
int dist(string a, string b) {
int res = 0;
for(int i = 0; i < a.length(); i++)
if(a[i] != b[i])
res++;
return res;
}
ll vol(int r) {
ll w = 0;
for(int i = 0; i <= r; i++)
w = (w + choose(n, i)) % m;
return w;
}
ll inter2(int r1, int r2, int d) {
int ones = d;
int zeroes = n - d;
ll w = vol(r2);
ll res = 0;
for(int i = r1 + 1; i <= min(r2 + ones, n); i++) {
int tmp = 0;
while(i - ones + 2*tmp <= r2 and i - ones + 2*tmp >= 0) {
res = (res + (choose(zeroes, i - ones + tmp) * choose(ones, tmp)) % m) % m;
tmp++;
}
}
return (w + m - res) % m;
}
ll inter3(int r1, int r2, int r3, string x1, string x2, string x3) {
ll c1 = 0, c2 = 0, c3 = 0, c4 = 0;
for(int i = 0; i < n; i++) {
if(x1[i] != x2[i] and x2[i] == x3[i]) c1++;
else if(x2[i] != x3[i] and x3[i] == x1[i]) c2++;
else if(x3[i] != x1[i] and x1[i] == x2[i]) c3++;
else if(x1[i] == x2[i] == x3[i]) c4++;
}
ll res = 0;
ll p1, p2, p3;
ll tmp;
for(int x = 0; x <= c1; x++) {
for(int y = 0; y <= c2; y++) {
for(int z = 0; z <= c3; z++) {
p1 = c1 - x + y + z;
p2 = c2 - y + x + z;
p3 = c3 - z + y + x;
if(p1 > r1 or p2 > r2 or p3 > r3)
continue;
tmp = min(r1 - p1, min(r2 - p2, r3 - p3));
res += choose(c4, min(c4,tmp));
res %= m;
}
}
}
return res;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
for(int i = 0; i < 10006; i++) {
facs[i] = facmod(i);
}
cin >> n;
int r1, r2, r3;
string x1, x2, x3;
cin >> r1 >> x1;
cin >> r2 >> x2;
cin >> r3 >> x3;
ll res = 3*m;
if((r1 == r2) and (x1 == x2)) {
res += vol(r3) + vol(r1);
res -= inter2(r1, r3, dist(x1, x3));
}
else if((r1 == r3) and (x1 == x3)) {
res += vol(r2) + vol(r3);
res -= inter2(r1, r2, dist(x1, x2));
}
else if((r2 == r3) and (x2 == x3)) {
res += vol(r2) + vol(r1);
res -= inter2(r2, r3, dist(x2, x3));
}
else {
res += (vol(r1) + vol(r2) + vol(r3));
res -= (inter2(r1, r2, dist(x1, x2)) + inter2(r1, r3, dist(x1, x3)) + inter2(r2, r3, dist(x2, x3)));
res += inter3(r1, r2, r3, x1, x2, x3);
}
cout << res % m << endl;
}
|