Decode Ways

You have intercepted a secret message encoded as a string of numbers. The message is **decoded** via the following mapping: `"1" -> 'A' "2" -> 'B' ... "25" -> 'Y' "26" -> 'Z'` However, while decoding the message, you realize that there are many different ways you can decode the message because some codes are contained in other codes (`"2"` and `"5"` vs `"25"`). For example, `"11106"` can be decoded into: - `"AAJF"` with the grouping `(1, 1, 10, 6)` - `"KJF"` with the grouping `(11, 10, 6)` - The grouping `(1, 11, 06)` is invalid because `"06"` is not a valid code (only `"6"` is valid). Note: there may be strings that are impossible to decode. Given a string s containing only digits, return the **number of ways** to **decode** it. If the entire string cannot be decoded in any valid way, return `0`. The test cases are generated so that the answer fits in a **32-bit** integer.   **Example 1:** **Input:** s = "12" **Output:** 2 **Explanation:** "12" could be decoded as "AB" (1 2) or "L" (12). **Example 2:** **Input:** s = "226" **Output:** 3 **Explanation:** "226" could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6). **Example 3:** **Input:** s = "06" **Output:** 0 **Explanation:** "06" cannot be mapped to "F" because of the leading zero ("6" is different from "06"). In this case, the string is not a valid encoding, so return 0.   **Constraints:** - `1 <= s.length <= 100` - `s` contains only digits and may contain leading zero(s).