Count and Say
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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
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.
题意:有一个整数序列 1,11,21,1211,111221,...
它是这样产生的:
1读作 ‘one 1’,即 11
11读作 ‘two 1s‘,即 21
21读作 ‘one 2 one 1‘,即1211
...
给定整数 n,返回该序列的第 n 个数
思路:模拟
复杂度:时间O(n),空间O(1)
//一般写法 string countAndSay(int n){ string last = "1"; while(--n){ int count = 1; char c = last[0]; string cur; for(int i = 1; i <= last.size(); ++i){ if(i < last.size() && last[i] == c) count++; else{ cur += count + '0'; cur += c; if(i < last.size()){ count = 1; c = last[i]; } } } last = cur; } return last; } //使用stl string countAndSay(int n){ string past = "1"; while(--n){ string cur; for(auto iter = past.begin(); iter != past.end();){ auto iter2 = find_if(iter, past.end(), bind1st(not_equal_to<char>(), *iter)); cur += distance(iter, iter2) + '0'; cur += *iter; iter = iter2; } past = cur; } return past; }
时间: 2024-10-11 07:06:20