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countAndSay.java
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54 lines (33 loc) · 1.17 KB
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// The count-and-say sequence is the sequence of integers beginning as follows:
// 1, 11, 21, 1211, 111221, ...
// 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, generate the nth sequence.
// Note: The sequence of integers will be represented as a string.
public class Solution {
public String countAndSay(int n) {
String s = "1";
for(int i = 1; i < n; i++) {
s = helper(s);
}
return s;
}
public String helper(String s) {
StringBuilder sb = new StringBuilder();
char c = s.charAt(0);
int count = 1;
for(int i = 1; i < s.length(); i++) {
if(s.charAt(i) == c) count++;
else {
sb.append(count);
sb.append(c);
c = s.charAt(i);
count = 1;
}
}
sb.append(count);
sb.append(c);
return sb.toString();
}
}