# 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.

```public class Solution {
public int numDecodings(String s) {
if (s.length() == 0) {
return 0;
}
int[] dp = new int[s.length()+1];
dp[0] = 1;
if (isValid(s.substring(0, 1))) {
dp[1] = 1;
} else {
dp[1] = 0;
}
for (int i = 2; i <= s.length(); i++) {
if (isValid(s.substring(i-1, i))) {
dp[i] = dp[i-1];
}
if (isValid(s.substring(i-2, i))) {
dp[i] += dp[i-2];
}
}
return dp[s.length()];
}

private boolean isValid(String substring) {
if (substring.charAt(0) == '0') {
return false;
}
int parseInt = Integer.parseInt(substring);
return parseInt>0 && parseInt<27;
}
}```

Decode Ways

• 0

开心

• 0

板砖

• 0

感动

• 0

有用

• 0

疑问

• 0

难过

• 0

无聊

• 0

震惊