91.解码方法

public static int numDecodings(String s) {
       if(s.length() == 0 || s == null || s.charAt(0)=='0'){
            return 0;
        }
        char[] arr = s.toCharArray();
        int[] arrInt = new int[arr.length];
        for(int i = 0 ; i < arr.length ; i ++){
            arrInt[i] = arr[i] - '1' + 1;
        }
        int num1 = 1,num2 = 1;
        int tmp = 1;
        for(int i = 1 ;i < arrInt.length ; i ++){
            tmp = num2;
            if(arrInt[i] == 0){
                if( arrInt[i-1] != 1 && arrInt[i-1]!=2)
                    return 0;
                else{
                    tmp = num1;
                }
            }else{
                if(arrInt[i-1]==1){
                    tmp = num1 + num2;
                }
                if(arrInt[i-1]==2 && arrInt[i] <= 6){
                    tmp = num1 + num2;
                }
            }

            num1=num2;
            num2 = tmp;
        }
        return tmp;

    }