mine （dp）

10.3

mine

思路：
简单dp

#include <cstdio>#include <cstring>#define LL long long #define N 5000010const LL mod = 1e9 + 7;int len;char s[N];LL f[N][5], ans = 0;//5种状态 0：以0结尾   1：以*1结尾   2：以1结尾(1前无*)   3：以2结尾   4：以*结尾 int main(){    freopen("mine.in","r",stdin);    freopen("mine.out","w",stdout);    scanf("%s", s+1);    len = strlen(s + 1);    f[0][0] = 1;    for(int i=1; i<=len; i++){        if(s[i]=='?' || s[i]=='0') f[i][0] = (f[i-1][0] + f[i-1][1]) % mod;        if(s[i]=='?' || s[i]=='1') f[i][1] = f[i-1][4], f[i][2] = (f[i-1][0] + f[i-1][1]) % mod;        if(s[i]=='?' || s[i]=='2') f[i][3] = f[i-1][4];        if(s[i]=='?' || s[i]=='*') f[i][4] = (f[i-1][4] + f[i-1][2] + f[i-1][3]) % mod;        if((s[i]=='?' || s[i]=='*') && i == 1) f[i][4] = 1;    }    ans = (f[len][0] + f[len][1] + f[len][4]) % mod;    printf("%I64d\n", ans);    return 0;}