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
class Solution {
public String countAndSay(int n) {
String res = "1";
for(int i=1;i<n;i++){
char[] c = res.toCharArray();
res="";
int count = 1;
for(int j=0;j<c.length-1;j++){
if(c[j]==c[j+1]){
count++;
}else{
res+=(""+count+c[j]);
count=1;
}
}
res+=(""+count+c[c.length-1]);
}
return res;
}
}