Package g0601_0700.s0639_decode_ways_ii

Class Solution

  • All Implemented Interfaces:
    
public final class Solution

    639 - Decode Ways II.

    Hard

    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".

    In addition to the mapping above, an encoded message may contain the '*' character, which can represent any digit from '1' to '9' ('0' is excluded). For example, the encoded message "1*" may represent any of the encoded messages "11", "12", "13", "14", "15", "16", "17", "18", or "19". Decoding "1*" is equivalent to decoding any of the encoded messages it can represent.

    Given a string s consisting of digits and '*' characters, return the number of ways to decode it.

    Since the answer may be very large, return it modulo <code>10<sup>9</sup> + 7</code>.

    Example 1:

    Input: s = "\*"

    Output: 9

    Explanation: The encoded message can represent any of the encoded messages "1", "2", "3", "4", "5", "6", "7", "8", or "9". Each of these can be decoded to the strings "A", "B", "C", "D", "E", "F", "G", "H", and "I" respectively. Hence, there are a total of 9 ways to decode "\*".

    Example 2:

    Input: s = "1\*"

    Output: 18

    Explanation: The encoded message can represent any of the encoded messages "11", "12", "13", "14", "15", "16", "17", "18", or "19". Each of these encoded messages have 2 ways to be decoded (e.g. "11" can be decoded to "AA" or "K"). Hence, there are a total of 9 \* 2 = 18 ways to decode "1\*".

    Example 3:

    Input: s = "2\*"

    Output: 15

    Explanation: The encoded message can represent any of the encoded messages "21", "22", "23", "24", "25", "26", "27", "28", or "29". "21", "22", "23", "24", "25", and "26" have 2 ways of being decoded, but "27", "28", and "29" only have 1 way. Hence, there are a total of (6 \* 2) + (3 \* 1) = 12 + 3 = 15 ways to decode "2\*".

    Constraints:

    • <code>1 <= s.length <= 10<sup>5</sup></code>

    • s[i] is a digit or '*'.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description

    • Field Summary

      Fields 
      Modifier and Type Field Description

    • Constructor Summary

      Constructors 
      Constructor Description
      Solution()

    • Enum Constant Summary

      Enum Constants 
      Enum Constant Description

    • Method Summary

      Modifier and Type Method Description
      final Integer numDecodings(String s)

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait