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.
curNum:代表当前数的解码数量
num2: 前一个数的解码数量
num1: 前两个数的解码数量
public int numDecodings(String s) { if (s == null || s.length() == 0 || s.charAt(0) == '0') return 0; int num1 = 1; int num2 = 1; int curNum = 1; for (int i = 1; i < s.length(); i++) { if (s.charAt(i) == '0') { if (s.charAt(i-1) == '1' || s.charAt(i-1) == '2') curNum = num1; else return 0; } else { if(s.charAt(i-1)=='1'||s.charAt(i-1)=='2'&&s.charAt(i)>='1'&&s.charAt(i)<='6') curNum = num1+num2; else curNum = num2; } num1=num2; num2=curNum; } return curNum; }
时间: 2024-10-10 07:31:56