Count And Say

Author: mengli

Count and Say.java

@@ -0,0 +1,38 @@
+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 nth sequence.
+
+Note: The sequence of integers will be represented as a string.
+
+public class Solution {
+    public String countAndSay(int n) {
+        StringBuilder s1 = new StringBuilder("1");
+        StringBuilder s2 = new StringBuilder();
+        for (int i = 1; i < n; i++) {
+            int j = 0;
+            int len = s1.length();
+            while (j < len) {
+                int count = 1;
+                char c = s1.charAt(j);
+                while (j < len - 1 && s1.charAt(j + 1) == s1.charAt(j)) {
+                    count++;
+                    j++;
+                }
+                s2.append(count + "");
+                s2.append(c);
+                if (j == len - 1) {
+                    break;
+                }
+                j++;
+            }
+            s1 = s2;
+            s2 = new StringBuilder();
+        }
+        return s1.toString();
+    }
+}