add 038

Author: andavid

README.md

@@ -38,6 +38,7 @@
 | 125  | [Valid Palindrome][125]                     |
 | 8    | [String to Integer (atoi)][008]             |
 | 28   | [Implement strStr()][028]                   |
+| 38   | [count-and-say][038]                        |
 
 
 **其他**
@@ -71,3 +72,4 @@
 [125]: https://github.com/andavid/leetcode-java/blob/master/note/125/README.md
 [008]: https://github.com/andavid/leetcode-java/blob/master/note/008/README.md
 [028]: https://github.com/andavid/leetcode-java/blob/master/note/028/README.md
+[038]: https://github.com/andavid/leetcode-java/blob/master/note/038/README.md

note/038/README.md

@@ -0,0 +1,73 @@
+# [count-and-say][title]
+
+## Description
+
+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"
+```
+
+## 思路
+遍历字符串，如果当前字符和上一个字符不相同，则输出计数情况，否则计数器加1。
+
+## [完整代码][src]
+
+```java
+class Solution {
+  public String countAndSay(int n) {
+    String str = "1";
+    for (int i = 1; i < n; i++) {
+      str = say(str);
+    }
+    return str;
+  }
+
+  public String say(String str) {
+    if (str.length() == 1) {
+      return "1" + str;
+    }
+    StringBuilder sb = new StringBuilder();
+    int count = 1;
+    int i = 1;
+    for (; i < str.length(); i++) {
+      if (str.charAt(i) != str.charAt(i - 1)) {
+        sb.append(count).append(str.charAt(i - 1));
+        count = 1;
+      } else {
+        count++;
+      }
+    }
+    sb.append(count).append(str.charAt(i - 1));
+    return sb.toString();
+  }
+}
+```
+
+[title]: https://leetcode.com/problems/count-and-say
+[src]: https://github.com/andavid/leetcode-java/blob/master/src/com/andavid/leetcode/_038/Solution.java

src/com/andavid/leetcode/_038/Solution.java

@@ -0,0 +1,34 @@
+class Solution {
+  public String countAndSay(int n) {
+    String str = "1";
+    for (int i = 1; i < n; i++) {
+      str = say(str);
+    }
+    return str;
+  }
+
+  public String say(String str) {
+    if (str.length() == 1) {
+      return "1" + str;
+    }
+    StringBuilder sb = new StringBuilder();
+    int count = 1;
+    int i = 1;
+    for (; i < str.length(); i++) {
+      if (str.charAt(i) != str.charAt(i - 1)) {
+        sb.append(count).append(str.charAt(i - 1));
+        count = 1;
+      } else {
+        count++;
+      }
+    }
+    sb.append(count).append(str.charAt(i - 1));
+    return sb.toString();
+  }
+
+  public static void main(String[] args) {
+    Solution solution = new Solution();
+    System.out.println(solution.countAndSay(1));
+    System.out.println(solution.countAndSay(8));
+  }
+}