【LeetCode】38. Count and Say

Difficulty:easy

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Description

https://leetcode.com/problems/count-and-say/

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

1.     1
2.     11
3.     21
4.     1211
5.     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 where 1 ≤ n ≤ 30, 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: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

Intuition

Straightforward

 

Solution

    public String countAndSay(int n) {
        String str="1";
        if(n==1)
            return str;
        while(n>1){
            str=getNext(str);
            n--;
        }
        return str;
    }
    
    private String getNext(String str){
        StringBuilder sb = new StringBuilder();
        int i=0;
        while(i<str.length()){
            char num=str.charAt(i);
            int count=0;
            while(i<str.length() && str.charAt(i)==num){
                i++;
                count++;
            }
            sb.append(count).append(num);
        }
        return sb.toString();
    }

　　

Complexity

 

 

What I've learned

 

 

 More:【目录】LeetCode Java实现