Count_and_say.java

38. Count and Say

@@ -0,0 +1,31 @@
+class Solution {
+    public String countAndSay(int n) {
+        if (n <= 0) {
+            throw new IllegalArgumentException("Invalid input");
+        }
+
+        StringBuilder sb = new StringBuilder("1");
+        for (int i = 2; i <= n; i++) {
+            sb = getNextState(sb);
+        }
+        return sb.toString();
+    }
+
+    private StringBuilder getNextState(StringBuilder curSb) {
+        StringBuilder nextSb = new StringBuilder();
+        int len = curSb.length();
+        int i = 0;
+
+        while (i < len) {
+            char c = curSb.charAt(i++);
+            int count = 1;
+            while (i < len && c == curSb.charAt(i)) {
+                count++;
+                i++;
+            }
+            nextSb.append(count).append(c);
+        }
+
+        return nextSb;
+    }
+}