class Solution {
    public int translateNum(int num) {
        char[] chars = Integer.toString(num).toCharArray();
        backtrack(chars, 0);
        return count;
    }
    int count = 0;

    public void backtrack(char[] num, int start) {
        if (start >= num.length) {
            count++;
            return;
        }
        //当本次是一个字符时
        String number = num[start] + "";
        backtrack(num, start + 1);

        //当本次是两个字符时
        if (start + 1 < num.length) {
            String number1 = num[start] + "" + num[start + 1];
            if (Integer.parseInt(number1) < 26) {
                if (Integer.parseInt(number1) != Integer.parseInt("" + num[start + 1])) {//去掉前缀零
                    backtrack(num, start + 2);
                }
            }

        }

    }
}

class Solution {
    public int translateNum(int num) {
        String s = String.valueOf(num);
        int[] dp = new int[s.length()+1];
        
        dp[0] = 1;
        dp[1] = 1;
        
        for(int i = 2; i <= s.length(); i ++){
            String temp = s.substring(i-2, i);
            if(temp.compareTo("10") >= 0 && temp.compareTo("25") <= 0)
                dp[i] = dp[i-1] + dp[i-2];
            else
                dp[i] = dp[i-1];
        }
        return dp[s.length()];
    }
}

class Solution {
    public int translateNum(int num) {
        String s = Integer.toString(num);
        int  last = 1, penultimate = 1,cur = last;//分别是上次计算的值，倒数第二次计算的值，和当前的值
        for (int i = 2; i <= s.length(); i++) {
            String str = s.substring(i - 2, i);
            if (str.compareTo("10") >= 0 && str.compareTo("25") <= 0) {
                cur = last + penultimate;
            } else {
                cur = last;
            }

            penultimate = last;//循环使用
            last = cur;
        }
        return cur;
    }
}