91. 解码方法

class Solution {
    public int numDecodings(String s) {
        if(s==null||s.equals("")){
            return 0;
        }
        char[] chas=s.toCharArray();
        int cur=chas[chas.length-1]=='0'?0:1;
        int next=1;
        int temp=0;
        for(int i=chas.length-2;i>=0;i--){
            if(chas[i]=='0'){
                next=cur;
                cur=0;
            }else{
                temp=cur;
                if((chas[i]-'0')*10+chas[i+1]-'0'<27){
                    cur+=next;
                }
                next=temp;
            }
        }
        return cur;
    }
}