# Count and Say

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. Following is an example to understand the problem better:

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`
```class Solution {
public String countAndSay(int n) {

String result = "1";
if(n == 1){
return result;
}
for(int i = 2 ; i <= n ; i++){
result = countAndSay(result);
}
return result;
}

private String countAndSay(String s){
char prev = s.charAt(0);
int count = 1;
int n = s.length();
StringBuilder result = new StringBuilder();
for(int i = 1 ; i < n ; i++){
char cur = s.charAt(i);
if(prev == cur){
count++;
}else{
result.append(count);
result.append(prev);
count = 1;
prev = cur;
}
}
result.append(count);
result.append(prev);
return result.toString();
}
}
```

Categories: String

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