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.
class Solution {
public:
int numDecodings(string s) {
if(s.empty() || s[0] == '0')
return 0;
int r1 = 1;
int r2 = 1;
for(int i = 1; s[i]; i++) {
if(s[i] == '0')
r1 = 0;
if(s[i-1] == '1' || (s[i-1] == '2' && s[i] <= '6'))
r1 += r2, r2 = r1 - r2;
else
r2 = r1;
}
return r1;
}
};