C++代码

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> b(n);
    for (int i = 0; i < n; ++i) {
        cin >> b[i];
    }
    
    if (n == 1) {
        cout << (b[0] == 0 || b[0] == 1 ? 1 : 0) << endl;
        return 0;
    }
    
    vector<vector<int>> prev_dp(2, vector<int>(2, 0));
    // 初始化i=0的情况
    for (int a0 = 0; a0 <= 1; ++a0) {
        for (int a1 = 0; a1 <= 1; ++a1) {
            if (a0 + a1 == b[0]) {
                prev_dp[a0][a1] = 1;
            }
        }
    }
    
    for (int i = 1; i < n - 1; ++i) {
        vector<vector<int>> curr_dp(2, vector<int>(2, 0));
        for (int p = 0; p <= 1; ++p) {
            for (int q = 0; q <= 1; ++q) {
                if (prev_dp[p][q] == 0) continue;
                int a_curr = b[i] - p - q;
                if (a_curr < 0 || a_curr > 1) continue;
                curr_dp[q][a_curr] += prev_dp[p][q];
                curr_dp[q][a_curr] %= 1000000007; // 防止溢出，题目未明确模数，但通常可能需要
            }
        }
        prev_dp = move(curr_dp);
    }
    
    int result = 0;
    for (int p = 0; p <= 1; ++p) {
        for (int q = 0; q <= 1; ++q) {
            if (p + q == b[n-1]) {
                result += prev_dp[p][q];
                result %= 1000000007;
            }
        }
    }
    
    cout << result << endl;
    return 0;
}