LeetCode 38. Count and Say

 1 package LeetCode;
 2 
 3 public class L38_CountAndSay {
 4     public String countAndSay(int n) {
 5         if(n<=0){
 6             return null;
 7         }
 8         String res="1";//第一行结果
 9         int len = 0;
10         for(int i=1;i<n;i++){//第二行及以后
11             int count=1;//数字出现次数
12             if(i==1){//第二行
13                 res="11";
14             }else {//不加else的计划，第二行有res，还会接着构建，第二行的res就会成为原本第三行展示的内容
15                 len = res.length();
16                 StringBuilder sb = new StringBuilder();
17                 for (int j = 1; j < len; j++) {//统计每个字符出现次数
18                     if (res.charAt(j - 1) == res.charAt(j)) {
19                         count++;
20                     } else {
21                         sb.append(count);
22                         sb.append(res.charAt(j - 1));
23                         count = 1;
24                     }
25                 }
26                 sb.append(count);
27                 sb.append(res.charAt(len - 1));
28                 res = sb.toString();
29             }
30         }
31         return res;
32     }
33     public static void main(String[] args){
34         L38_CountAndSay l38=new L38_CountAndSay();
35         System.out.println(l38.countAndSay(4));
36     }
37 }