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DecodeNumber.java
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59 lines (55 loc) · 1.66 KB
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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.
*/
public class DecodeNumber {
public static void main(String[] args) {
String s1 = "11";
String s2 = "2119";
String s3 = "116";
decodeNumber(s1);
decodeNumber(s2);
decodeNumber(s3);
}
public static void decodeNumber(String s) {
int len = s.length();
if (len == 0) {
System.out.println("empty string");
return;
}
for (int i = 0; i < len; i++) {
if (!((s.charAt(i) - '0') <= 9) && !(('9' - s.charAt(i)) >= 0)) {
System.out.println(s + " is not number.");
return;
}
}
int[] ways = new int[len];
ways[0] = (s.charAt(0) == '0') ? 0 : 1;
for (int i = 1; i < len; i++) {
char p = s.charAt(i - 1);
char c = s.charAt(i);
if (p !='0' && ways[i - 1] == 0)
ways[i] = 1;
if ( ways[i-1] != 0) {
ways[i] = ways[i-1];
}
if (p == '1' || (p == '2' && c <= '6')) {
if(i>=2)
ways[i] = ways[i - 2] + ways[i];
else
ways[i] = ways[i-1] + ways[i];
}
}
System.out.println(s + ":" + ways[len - 1]);
}
}