Java for LeetCode 091 Decode Ways

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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()];

	}