add solution of problem 38: count and say

Author: ppulse

CountAndSay38/README.md

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+The count-and-say sequence is the sequence of integers beginning as follows:
+`1, 11, 21, 1211, 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 n<sup>th</sup> sequence.
+
+Note: The sequence of integers will be represented as a string.

CountAndSay38/Solution.java

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+public class Solution {
+    public String countAndSay(int n) {
+        String last = "1";
+        
+        for (int i = 1; i < n; i++) {
+            StringBuilder sb = new StringBuilder();
+            int j = 0;
+            while (j < last.length()) {
+                int cnt = 1;
+            
+                while (j + 1 < last.length() && last.charAt(j + 1) == last.charAt(j)) {
+                    j++;
+                    cnt++;
+                }
+            
+                sb.append(cnt).append(last.charAt(j));
+                j++;
+            }
+            
+            last = sb.toString();
+        }
+        
+        return last;
+    }
+}