639. Decode Ways II

// 639. Decode Ways II
// 37ms
// 39.7mb

class Solution {
    public int numDecodings(String s) {
        long[] dp=new long[s.length()+1];
        dp[0]=1;
        dp[1]=decodeOneChar(s.charAt(0));
        
        for(int i=2;i<=s.length();i++){
            
            dp[i]+=dp[i-1]*decodeOneChar(s.charAt(i-1));
            dp[i]+=dp[i-2]*decodeTwoChar(s.charAt(i-2),s.charAt(i-1));
            
            dp[i]=dp[i]%1000000007;
        }
        return (int)dp[s.length()];
        
    }
    
    public int decodeOneChar(char c){
        if(c=='*')
            return 9;
        else if(c=='0')
            return 0;
        
        return 1;
    }
    
    
    public int decodeTwoChar(char first,char second){
        switch(first){
            case '*' :
                if(second=='*')
                    return 15;
                else if(second>='0' && second<='6')
                    return 2;
                else 
                    return 1;
                
            case '1' :
                if(second=='*')
                    return 9;
                else 
                    return 1;
                
            case '2' :
                if(second=='*')
                    return 6;
                else if(second>='0' && second<='6')
                    return 1;
                else 
                    return 0;
                
            default:
                return 0;
        }
    }
}