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()];
}
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