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.
Solution:O(n)
public class Solution { public String countAndSay(int n) { String s = "1"; for(int i=1; i<n;i++){ s = getString(s); } return s; } public String getString(String s){ if(s.length() == 1){ return "1"+s; } String ret = ""; char cur = s.charAt(0); int count = 1; for(int i=1; i< s.length();i++){ if(s.charAt(i) == cur) count++; else{ ret = ret + count+ cur; count = 1; cur = s.charAt(i); } } ret = ret + count+ cur; return ret; } }
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