【剑指Offer】46. 把数字翻译成字符串

class Solution {
    public int translateNum(int num) {
            String s = String.valueOf(num);
            // 0 ~ 25 
            // 动态规划 dp[i] = dp[i-1] + (dp[i-2])
            int a = 1, b = 1;
            for(int i = 2; i <= s.length(); i++) {
                String temp = s.substring(i - 2, i);
                int c =temp.compareTo("10") >= 0 && temp.compareTo("25") <= 0 ? a+b : a;
                b = a;
                a = c;
            }
            return a;
    }
}

public int numDecodings(String s) {
    if (s == null || s.length() == 0)
        return 0;
    int n = s.length();
    int[] dp = new int[n + 1];
    dp[0] = 1;
    dp[1] = s.charAt(0) == '0' ? 0 : 1;
    for (int i = 2; i <= n; i++) {
        int one = Integer.valueOf(s.substring(i - 1, i));
        if (one != 0)
            dp[i] += dp[i - 1];
        if (s.charAt(i - 2) == '0')
            continue;
        int two = Integer.valueOf(s.substring(i - 2, i));
        if (two <= 26)
            dp[i] += dp[i - 2];
    }
    return dp[n];
}