-
Notifications
You must be signed in to change notification settings - Fork 22
Expand file tree
/
Copy path91.decode-ways.py
More file actions
62 lines (57 loc) · 1.7 KB
/
91.decode-ways.py
File metadata and controls
62 lines (57 loc) · 1.7 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
# Tag: String, Dynamic Programming
# Time: O(N)
# Space: O(N)
# Ref: -
# Note: -
# 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 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").
#
#
# Constraints:
#
# 1 <= s.length <= 100
# s contains only digits and may contain leading zero(s).
#
#
class Solution:
def numDecodings(self, s: str) -> int:
n = len(s)
dp = [0 for i in range(n + 1)]
dp[0] = 1
for i in range(1, n + 1):
if s[i - 1] != '0':
dp[i] += dp[i - 1]
if i - 2 >= 0 and (s[i - 2] == '1' or s[i - 2] == '2' and int(s[i - 1]) <= 6):
dp[i] += dp[i - 2]
return dp[n]