Java for LeetCode 091 Decode Ways

A message containing letters from A-Z is being encoded to numbers using the following mapping:

'A' -> 1
'B' -> 2
...
'Z' -> 26

Given an encoded message containing digits, determine the total number of ways to decode it.

For example,
Given encoded message "12", it could be decoded as "AB" (1 2) or "L" (12).

The number of ways decoding "12" is 2.

解题思路：

dp问题，JAVA实现如下：

		static public int numDecodings(String s) {
		if (s.length() == 0 || s.charAt(0) == '0')
			return 0;
		int[] dp = new int[s.length() + 1];
		dp[0] = dp[1] = 1;
		for (int i = 1; i < s.length(); i++) {
			if (s.charAt(i) == '0'&& (s.charAt(i - 1) != '1' && s.charAt(i - 1) != '2'))
				return 0;
			else if (s.charAt(i) == '0')
				dp[i + 1] = dp[i - 1];
			else if (s.charAt(i - 1) == '0'||(s.charAt(i-1)-'0')*10+(s.charAt(i)-'0')>26)
				dp[i + 1] = dp[i];
			else
				dp[i + 1] = dp[i - 1] + dp[i];
		}
		return dp[s.length()];
	}