91. Decode Ways
https://leetcode.com/problems/decode-ways/
Time - O(2 ^ N) - 2 branching at each recursive call - pure DFS
Time - O(N) - each index is visited only once - memoized
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A message containing letters from
A-Z is being encoded to numbers using the following mapping:'A' -> 1 'B' -> 2 ... 'Z' -> 26
Given a non-empty string containing only digits, determine the total number of ways to decode it.
Example 1:
Input: "12" Output: 2 Explanation: It could be decoded as "AB" (1 2) or "L" (12).
Example 2:
Input: "226" Output: 3 Explanation: It could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).---
Time - O(2 ^ N) - 2 branching at each recursive call - pure DFS
Time - O(N) - each index is visited only once - memoized
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