38. 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, 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"//翻译题意思：题意是n=1时输出字符串1；n=2时，数上次字符串中的数值个数，因为上次字符串有1个1，所以输出11；n=3时，由于上次字符是11，有2个1，所以输出21；n=4时，由于上次字符串是21，有1个2和1个1，所以输出1211。依次类推， class Solution { public String countAndSay(int n) { if (n <= 0) return "-1"; String result = "1"; for (int i = 1; i < n; i++) result = build(result); return result; } private String build(String result) { StringBuilder sb = new StringBuilder(); int p = 0; while (p < result.length()) { char val = result.charAt(p); int count = 0; while (p < result.length() && result.charAt(p) == val) { p++; //当出现重复数字，坐标加一，count也加一 count++; } sb.append(String.valueOf(count)); sb.append(val); } return sb.toString(); } }
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