标签：style blog color io for re c 问题
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.
题解：DP问题。
对于s中位置i(s[i] != ‘0‘)上的字符，有两种可能：
代码如下：
1 public class Solution { 2 private boolean isValidNum(String s,int i){ 3 if(i <= 0) 4 return false; 5 int first = s.charAt(i-1)-‘0‘; 6 int second = s.charAt(i)-‘0‘; 7 int num = first*10 + second; 8 if(num >= 10 && num <= 26) 9 return true; 10 return false; 11 } 12 public int numDecodings(String s) { 13 if(s==null || s.length() == 0) 14 return 0; 15 int length = s.length(); 16 int[] dp = new int[length+1]; 17 18 dp[0] = 1; 19 dp[1] = s.charAt(0) == ‘0‘?0:1; 20 21 for(int i=2;i<=length;i++){ 22 if(s.charAt(i-1) != ‘0‘) 23 dp[i]=dp[i-1]; 24 25 if(isValidNum(s, i-1)) 26 dp[i] += dp[i-2]; 27 } 28 return dp[length]; 29 } 30 }
【leetcode刷题笔记】Decode Ways,布布扣,bubuko.com
标签：style blog color io for re c 问题
原文地址：http://www.cnblogs.com/sunshineatnoon/p/3865991.html
