(算法分析Week4)Count and Say[Easy]

38. Count and Say

Description

The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     12.     113.     214.     12115.     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 term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1Output: "1"

Example 2:

Input: 4Output: "1211"

Solution

这道题题意个人感觉不是很清晰，实际上是想让你根据已经给出的string构造新的string，构造规则就是count and say.当输入为6的时候，应该根据5“111221”构造新的“three one two two one one”即312211.了解了题目的意思之后就很简单了，从第二个string开始构造，每次循环重复，不是难题，具体还是看代码。

Complexity analysis

O（n²）

Code

class Solution {public:    string countAndSay(int n) {        if (n == 1)            return "1";        string result = "1";        for (int i = 1; i < n; i++) {            string temp = "";            char count = '1';            for (int j = 1; j < result.size(); j++) {                if (result[j] == result[j-1]) {                    count++;                } else {                  //  temp += count + result[j-1];                  //这里遇到了坑...忘记优先级，卡了很久                    temp += count;                    temp += result[j-1];                    count = '1';                }            }            result = temp + count + result[result.size() - 1];        }        return result;    }};

Result