public class Solution {
public int numDecodings(String s) {
if(s.length()==0) return 0;
int[] dp=new int[s.length()+1];
dp[s.length()]=1;
dp[s.length()-1]= s.charAt(s.length()-1)!='0'? 1:0;
for(int i=s.length()-2;i>=0;i--){
if(s.charAt(i)=='0') continue;
else dp[i]= (Integer.parseInt(s.substring(i,i+2))<=26)? dp[i+1]+dp[i+2]:dp[i+1];
}
return dp[0];
}
}
public class Solution {
public int numDecodings(String s) {
int n1 =1, n2=1, n3=0;
if(s.length()==0||s.charAt(0)=='0') return 0;
for(int i=2; i<=s.length(); i++)
{
n3=0;
if(s.charAt(i-1)!='0') n3=n2;
int num = Integer.parseInt(s.substring(i-2,i));
if(num>=10 && num<=26) n3+=n1;
n1=n2;
n2=n3;
}
return n2;
}
}
