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DecodeWays.java
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DecodeWays.java
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/**
* A message containing letters from A-Z is being encoded to numbers using the following mapping:
* <p>
* 'A' -> 1
* 'B' -> 2
* ...
* 'Z' -> 26
* Given an encoded message containing digits, determine the total number of ways to decode it.
* <p>
* For example,
* Given encoded message "12", it could be decoded as "AB" (1 2) or "L" (12).
* <p>
* The number of ways decoding "12" is 2.
* <p>
* Accepted.
*/
public class DecodeWays {
public int numDecodings(String s) {
if (s == null || s.isEmpty() || s.charAt(0) == '0') {
return 0;
}
int[] ints = new int[s.length() + 1];
ints[0] = 1;
for (int i = 1; i < ints.length; i++) {
ints[i] = s.charAt(i - 1) == '0' ? 0 : ints[i - 1];
if (i > 1 && (s.charAt(i - 2) == '1' || (s.charAt(i - 2) == '2') && s.charAt(i - 1) <= '6')) {
ints[i] += ints[i - 2];
}
}
return ints[s.length()];
}
}