The count-and-say sequence is the sequence of integers beginning as follows:1, 11, 21, 1211, 111221, ...
1
is read off as "one
or
1"11
.11
is read off as "two
or
1s"21
.21
is read off as "one
, then
2one 1"
or 1211
.
Given an integer n, generate the nth sequence.
Note: The sequence of integers will be represented as a string.
此算法在leetcde上实际执行时间为3ms。
class Solution { public: string countAndSay(int n) { if (n < 1) return ""; string result("1"); while (--n) { stringstream stream; char last = result[0]; int count = 1; for (int i=1; i<result.size(); i++) { if (result[i] == last) count++; else { stream << count << last; last = result[i]; count = 1; } } stream << count << last; result = stream.str(); } return result; } };