leetcode刷题-Count and Say

淡淡的烟草味﹌ 2023-01-09 03:43 106阅读 0赞

# 题目 #

地址：https://leetcode-cn.com/problems/count-and-say/  
描述：The count-and-say sequence is a sequence of digit strings defined by the recursive formula:

countAndSay(1) = “1”  
countAndSay(n) is the way you would “say” the digit string from countAndSay(n-1), which is then converted into a different digit string.  
To determine how you “say” a digit string, split it into the minimal number of groups so that each group is a contiguous section all of the same character. Then for each group, say the number of characters, then say the character. To convert the saying into a digit string, replace the counts with a number and concatenate every saying.

# 代码 #

class Solution {
        public String countAndSay(int n) {
            if (n == 1) {
                return "1";
            }
            StringBuilder sb = new StringBuilder(n * 2);
            sb.append("1");
            for (int i = 2; i <= n; i++) {
                countAndSay1(sb.toString(), sb.delete(0, sb.length()));
            }
            return sb.toString();
        }
        private void countAndSay1(String n, StringBuilder sb) {
            char pre = n.charAt(0);
            int count = 1;
            for (int i = 1; i < n.length(); i++) {
                char cur = n.charAt(i);
                if (cur != pre) {
                    sb.append(count).append(pre);
                    pre = cur;
                    count = 1;
                } else {
                    count++;
                }
            }
            sb.append(count).append(pre);
        }
    }

# 结果 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NuZGF5WVU_size_16_color_FFFFFF_t_70]

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