CF404D Minesweeper 1D

說明見：https://github.com/CyberZHG/blog/issues/10

#include <cstdio>const int MAXN = 1e6 + 10;const int MOD = 1e9 + 7;int dp[MAXN][5];char s[MAXN];int main(){    int n;    scanf("%s", s);    switch (s[0])    {    case '?':        dp[0][0] = dp[0][2] = dp[0][4] = 1;        break;    case '*':        dp[0][4] = 1;        break;    case '0':        dp[0][0] = 1;        break;    case '1':        dp[0][2] = 1;        break;    }    int i;    for (i = 1; s[i]; ++i)    {        switch (s[i])        {        case '?':            dp[i][0] = (dp[i - 1][0] + dp[i - 1][1]) % MOD;            dp[i][1] = dp[i - 1][4];            dp[i][2] = (dp[i - 1][0] + dp[i - 1][1]) % MOD;            dp[i][3] = dp[i - 1][4];            dp[i][4] = ((dp[i - 1][2] + dp[i - 1][3]) % MOD + dp[i - 1][4]) % MOD;            break;        case '*':            dp[i][4] = ((dp[i - 1][2] + dp[i - 1][3]) % MOD + dp[i - 1][4]) % MOD;            break;        case '0':            dp[i][0] = (dp[i - 1][0] + dp[i - 1][1]) % MOD;            break;        case '1':            dp[i][1] = dp[i - 1][4];            dp[i][2] = (dp[i - 1][0] + dp[i - 1][1]) % MOD;            break;        case '2':            dp[i][3] = dp[i - 1][4];            break;        }    }    --i;    printf("%d\n", ((dp[i][0] + dp[i][1]) % MOD + dp[i][4]) % MOD);    return 0;}