A message containing letters from A-Z is being encoded to numbers using the following mapping:
‘A‘ -> 1 ‘B‘ -> 2 ... ‘Z‘ -> 26
Given a non-empty string containing only digits, determine the total number of ways to decode it.
Example 1:
Input: "12" Output: 2 Explanation: It could be decoded as "AB" (1 2) or "L" (12).
Example 2:
Input: "226" Output: 3 Explanation: It could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).
class Solution { public int numDecodings(String s) { if(s == null || s.length() == 0) return 0; int len = s.length(); int[] dp = new int[len + 1]; dp[0] = 1; dp[1] = s.charAt(0) != ‘0‘ ? 1 : 0; for(int i = 2; i <= len; i++){ int first = Integer.valueOf(s.substring(i - 1, i)); int second = Integer.valueOf(s.substring(i - 2, i)); if(first >= 1 && first <= 9){ dp[i] += dp[i-1]; } if(second >= 10 && second <= 26){ dp[i] += dp[i-2]; } } return dp[len]; } }
https://www.cnblogs.com/grandyang/p/4313384.html
原文：https://www.cnblogs.com/wentiliangkaihua/p/11677104.html