Package g0001_0100.s0091_decode_ways

Class Solution

java.lang.Object
g0001_0100.s0091_decode_ways.Solution
public class Solution extends Object
91 - Decode Ways\. Medium A message containing letters from `A-Z` can be **encoded** into numbers using the following mapping: 'A' -> "1" 'B' -> "2" ... 'Z' -> "26" To **decode** an encoded message, all the digits must be grouped then mapped back into letters using the reverse of the mapping above (there may be multiple ways). For example, `"11106"` can be mapped into: * `"AAJF"` with the grouping `(1 1 10 6)` * `"KJF"` with the grouping `(11 10 6)` Note that the grouping `(1 11 06)` is invalid because `"06"` cannot be mapped into `'F'` since `"6"` is different from `"06"`. Given a string `s` containing only digits, return _the **number** of ways to **decode** it_. The answer is guaranteed to fit 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 = "0" **Output:** 0 **Explanation:** There is no character that is mapped to a number starting with 0. The only valid mappings with 0 are 'J' -> "10" and 'T' -> "20", neither of which start with 0. Hence, there are no valid ways to decode this since all digits need to be mapped. **Example 4:** **Input:** s = "06" **Output:** 0 **Explanation:** "06" cannot be mapped to "F" because of the leading zero ("6" is different from "06"). **Constraints:** * `1 <= s.length <= 100` * `s` contains only digits and may contain leading zero(s).

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • numDecodings

      public int numDecodings(String s)