typedef long long ll
2024-01-01 20:52:09
发布于:广东
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#include <iostream>
#include <cstring>
const int mo = 1000000007;
typedef long long ll;
using namespace std;
char c[100001];
ll f[100001][4][4][4], ans;
int n;
int get_bh(char x) {
if (x == 'A') return 0;
if (x == 'C') return 1;
if (x == 'G') return 2;
return 3;
}
int main() {
cin>>c+1;
n = strlen(c + 1);
if (c[1] == '?') {
for (int i = 0; i < 4; i++)
for (int j = 0; j < 4; j++)
f[1][i][i][j] = 1;
}
else {
for (int j = 0; j < 4; j++)
f[1][get_bh(c[1])][get_bh(c[1])][j] = 1;
}
for (int i = 2; i <= n; i++)
for (int j = 0; j < 4; j++)
for (int k = 0; k < 4; k++)
for (int l = 0; l < 4; l++) {
int now = get_bh(c[i]);
if (c[i] == '?') {
for (now = 0; now < 4; now++) {
if (now != k) {
f[i][j][now][l] = (f[i][j][now][l] + f[i - 1][j][k][l]) % mo;
}
if (k == l) {
f[i][now][now][j] = (f[i][now][now][j] + f[i - 1][j][k][l]) % mo;
}
}
}
else {
if (now != k) {
f[i][j][now][l] = (f[i][j][now][l] + f[i - 1][j][k][l]) % mo;
}
if (k == l) {
f[i][now][now][j] = (f[i][now][now][j] + f[i - 1][j][k][l]) % mo;
}
}
}
for (int j = 0; j < 4; j++)
for (int k = 0; k < 4; k++)
ans = (ans + f[n][j][k][k]) % mo;
cout<<ans;
return 0;
}
这里空空如也
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