Solution.java

class Solution {
    private static final int N = 100010;
    private static final int MOD = (int) 1e9 + 7;
    private static long[] f = new long[N];
    private static long[] g = new long[N];
    static {
        f[0] = 1;
        f[1] = 1;
        f[2] = 2;
        f[3] = 4;
        g[0] = 1;
        g[1] = 1;
        g[2] = 2;
        g[3] = 4;
        for (int i = 4; i < N; ++i) {
            f[i] = (f[i - 1] + f[i - 2] + f[i - 3]) % MOD;
            g[i] = (g[i - 1] + g[i - 2] + g[i - 3] + g[i - 4]) % MOD;
        }
    }

    public int countTexts(String pressedKeys) {
        long ans = 1;
        for (int i = 0, n = pressedKeys.length(); i < n; ++i) {
            int j = i;
            char c = pressedKeys.charAt(i);
            for (; j + 1 < n && pressedKeys.charAt(j + 1) == c; ++j)
                ;
            int cnt = j - i + 1;
            ans = c == '7' || c == '9' ? ans * g[cnt] : ans * f[cnt];
            ans %= MOD;
            i = j;
        }
        return (int) ans;
    }
}