LeetCode-Count and Say

Count and Say

##题目

####Count and Say

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.

##解题思路
该题是输出上述字符串序列中第n个字符串的问题。该题在生成字符串的过程中，需要首先放入元素的出现次数，然后在放入该元素。因此后一个字符串的生成，需要对前一个字符串统计元素的出现次数问题。

在实现的过程中，需要小心最后一个元素有没有放入的问题。

##算法代码
代码采用JAVA实现：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
public class Solution {
    public String countAndSay(int n) {
        if(n<1)
        	return "";
        if(n==1)
        	return "1";
        String cur="1";
        for(int i=2;i<=n;i++)
        {
        	StringBuilder result=new StringBuilder();
	        int count=1;
        	for(int j=1;j<cur.length();j++)
	        {
	    	 	if(cur.charAt(j)==cur.charAt(j-1))  //统计出现次数
	    	 		count++;
	    	 	else{                                //放入结果字符串中
	    	 		result.append(count);
	    	 		result.append(cur.charAt(j-1));
	    	 		count=1;
	    	 	}
	        }
			//最后一个字符没有放入结果字符串中
	        result.append(count);
	        result.append(cur.charAt(cur.length()-1));
	        cur=result.toString();
        }
        return cur;      
    }
}

Comments

▲