A message containing letters from A-Z is being encoded to numbers using the following mapping:
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| 'A' -> 1
'B' -> 2
...
'Z' -> 26
|
样例
Given encoded message 12, it could be decoded as AB (1 2) or L (12).
The number of ways decoding 12 is 2.
Given an encoded message containing digits, determine the total number of ways to decode it.
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| public class Solution {
* @param s a string, encoded message
* @return an integer, the number of ways decoding
*/
public int numDecodings(String s) {
if(null == s || s.length() <= 0)
return 0;
if(s.length() == 1 && s.charAt(0) == '0')
return 0;
int[] numDecodings = new int[s.length() + 1];
numDecodings[0] = 1;
for(int i = 1;i <= s.length();i++)
{
if(s.charAt(i - 1) == '0')
{
if(i- 2 >= 0)
{
if(s.charAt(i - 2) != '1' && s.charAt(i - 2) != '2')
{
return 0;
}
else
{
numDecodings[i] += numDecodings[i - 2];
continue;
}
}
}
numDecodings[i] += numDecodings[i - 1];
if(i - 2 >= 0)
{
if((s.charAt(i - 2) == '1') || (s.charAt(i - 2) == '2'
&& s.charAt(i - 1) >= '1' && s.charAt(i - 1) <= '6'))
{
numDecodings[i] += numDecodings[i - 2];
}
}
}
return numDecodings[s.length()];
}
}
|