[leetcode] Count and Say

原创于 2013-04-12 14:05:02 发布 · 138 阅读

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本文介绍了一种名为“计数并说”的整数序列，并提供了一个递归解决方案来生成给定位置的序列。该序列从1开始，后续每一项都是前一项的描述。例如，1读作“一1”或11；11读作“两1”或21。通过Java实现的方法展示了如何递归地构建这个序列。

http://leetcode.com/onlinejudge#question_38

Question:

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.

Solution:

Recursive.


public class Solution {
    public String countAndSay(int n) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int i = 1;
        String[] result = new String[n];
        while(i<=n){
            if(i==1){
                result[i-1] = "1";
            }else {
                getNext(result, i-1);
            }
            i++;
        }
        return result[n-1];
    }

    public void getNext(String[] aray, int index){
        String cur = aray[index-1];
        String next = "";
        for(int i=0; i< cur.length();){

            int j = i;
            while(j<cur.length()){
                if(cur.charAt(j) == cur.charAt(i)){
                    j++;
                }else {
                    break;
                }    
            }

            next += j-i;
            next += cur.charAt(i);
            i=j;
        }
        aray[index] = next;
    }
}