The count-and-say sequence is the sequence of integers with the first five terms as following:
1
2
3
4
5
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1. 1
2. 11
3. 21
4. 1211
5. 111221
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1 is read off as "one 1" or 11.
11 is read off as "two 1s" or 21.
21 is read off as "one 2, then one 1" or 1211.
Given an integer n where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.
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2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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18
19
20
21
22
23
24
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class {
public String countAndSay(int n) {
assert n > 0;
StringBuilder currSeq = new StringBuilder("1");
for (int i = 1; i < n; i++) {
currSeq = getNextSeq(currSeq);
}
return currSeq.toString();
}
private static StringBuilder getNextSeq(StringBuilder seq) {
StringBuilder nextSeq = new StringBuilder();
int cnt = 1;
for (int i = 0; i < seq.length(); i++) {
if (i + 1 < seq.length() && seq.charAt(i) == seq.charAt(i + 1)) {
cnt++;
} else {
nextSeq.append(cnt).append(seq.charAt(i));
cnt = 1;
}
}
return nextSeq;
}
}
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