LeetCode91:Decode Ways
A message containing letters from A-Z
is being encoded to numbers using the following mapping:
'A' -> 1 'B' -> 2 ... 'Z' -> 26
Given an encoded message containing digits, determine the total number of ways to decode it.
For example,
Given encoded message "12"
, it could be decoded as "AB"
(1 2) or "L"
(12).
The number of ways decoding "12"
is 2.
这道题的关键是如何进行分类的问题。
设状态A[i]表示字符串前i个字符能表示的解码个数。那么它依赖于A[i-1]和A[i-2]。具体的依赖关系如下图: