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CountAndSay.java
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CountAndSay.java
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package Leetcode;
/**
* @author kalpak
*
* The count-and-say sequence is a sequence of digit strings defined by the recursive formula:
*
* countAndSay(1) = "1"
* countAndSay(n) is the way you would "say" the digit string from countAndSay(n-1),
* which is then converted into a different digit string.
*
* To determine how you "say" a digit string,
* split it into the minimal number of groups so that each group is a contiguous section all of the same character.
* Then for each group, say the number of characters, then say the character.
* To convert the saying into a digit string, replace the counts with a number and concatenate every saying.
*
* For example, the saying and conversion for digit string "3322251":
*
*
* Given a positive integer n, return the nth term of the count-and-say sequence.
*
* Example 1:
* Input: n = 1
* Output: "1"
* Explanation: This is the base case.
*
*
* Example 2:
* Input: n = 4
* Output: "1211"
* Explanation:
* countAndSay(1) = "1"
* countAndSay(2) = say "1" = one 1 = "11"
* countAndSay(3) = say "11" = two 1's = "21"
* countAndSay(4) = say "21" = one 2 + one 1 = "12" + "11" = "1211"
*
*
* Constraints:
*
* 1 <= n <= 30
*/
public class CountAndSay {
public static String countAndSay(int n) {
String result = "1";
for(int i = 1; i < n; i++)
result = getSequence(result);
return result;
}
private static String getSequence(String result) {
StringBuilder sb = new StringBuilder();
char currentCh = result.charAt(0);
int count = 1;
for(int i = 1; i < result.length(); i++) {
if(result.charAt(i) == currentCh)
count++;
else {
sb.append(count);
sb.append(currentCh);
count = 1;
currentCh = result.charAt(i);
}
}
sb.append(count);
sb.append(currentCh);
return sb.toString();
}
public static void main(String[] args) {
System.out.println(countAndSay(6));
}
}