外观数组(leetcode38)

package com.vincent.leetcode;

public class leetcode38 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        int n=8;
        System.out.println(countAndSay1(n));
    }

    
    //循环
    public static String countAndSay(int n) {
        
         if(n==1){
            return "1";
        }
        
        int i=1;
        StringBuilder result = new StringBuilder();
        StringBuilder preResult = new StringBuilder();
        preResult.append("1");
        for(;i<n;i++){
            Character ch;
            int count=1;
            int j=0;
            for(;j<preResult.length()-1;j++){
                ch = preResult.charAt(j);
if(preResult.charAt(j+1)==preResult.charAt(j)){//如果j位置的字符与j+1位置的字符相同，则count加1
                    count++;
                }else{//如果j和j+1位置的字符不同，则说明可以把该字符的个数和该字符加入结果了，然后count重置为1,开始统计下个字符连续出现的数量
                    result.append(count);
                    result.append(ch);
                    count=1;
                }
            }
            if(j<preResult.length()){//加入最后一个字符及它的个数
                result.append(count);
                result.append(preResult.charAt(preResult.length()-1));
            }
            preResult.delete(0, preResult.length());//清理上一个结果
            preResult.append(result.toString());
            result.delete(0, result.length());
        }
        return preResult.toString();
    }
    
    //循环
    public static String countAndSay1(int n) {
        
        StringBuilder preResult = new StringBuilder();
        //记录当前行的字符串，即n为i时对应的字符串
        StringBuilder result = new StringBuilder();
        preResult.append(1);
        for(int i=1;i<n;i++){
            
            //记录每个数字的开始索引
            int start = 0;
            for(int j=1;j<preResult.length();j++){
                //当数字发生改变时执行
                if(preResult.charAt(j)!=preResult.charAt(start)){
                    result.append(j-start).append(preResult.charAt(start));
                    start = j;
                }
            }
            //字符串最后一个字符，可以考虑i=1时；
            result.append(preResult.length()-start).append(preResult.charAt(start));
            preResult.delete(0, preResult.length());
            preResult.append(result);
            result.delete(0, result.length());
            
        }
        
        return preResult.toString();
    }
    
    //递归
    public static String countAndSay2(int n) {
        //递归终止条件
        if(n==1){
            return "1";
        }
        //获取到上一层的字符串
        String preResult = countAndSay2(n-1);
        StringBuilder result = new StringBuilder();
        //记录每个数字的开始索引
        int start = 0;
        for(int i=1;i<preResult.length();i++){
            //当数字发生改变时执行
            if(preResult.charAt(i)!=preResult.charAt(start)){
                result.append(i-start).append(preResult.charAt(start));
                start = i;
            }
        }
        //字符串最后一个数字
        result.append(preResult.length()-start).append(preResult.charAt(start));
        return result.toString();
    }
}