update

Author: xiaoyaoworm

.DS_Store

@@ -1,26 +1,34 @@
 public class Solution {
     public String countAndSay(int n) {
-        if(n<=0) return null;
-        String result = "1";
-        if(n==1) return result;
-        for(int i = 2; i<= n; i++){
-            StringBuffer sb = new StringBuffer();
-            char prev = result.charAt(0);
-            int count = 1;
-            for(int j = 1; j < result.length(); j++){
-                char next = result.charAt(j);
-                if(next == prev) count++;
-                else{
-                    sb.append(count);
-                    sb.append(prev);
-                    prev = next;
-                    count = 1;
-                }
+        String s = "1";
+        for(int i = 1; i<n;i++){
+            s = helper(s);
+        }
+        return s;
+    }
+    
+    public String helper(String s){
+        StringBuffer sb = new StringBuffer();
+        
+        int count = 1;
+        char c = s.charAt(0);
+        
+        int i = 1;
+        while(i< s.length()){
+            if(s.charAt(i) == c){
+                count++;
+            }
+            else{
+                sb.append(count);
+                sb.append(c);
+                count = 1;
+                c = s.charAt(i);
             }
-            sb.append(count);
-            sb.append(prev);
-            result = sb.toString();
+            i++;
         }
-        return result;
+        sb.append(count);
+        sb.append(c);
+        
+        return sb.toString();
     }
 }

38_countAndSay.java

@@ -0,0 +1,26 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+public class Solution {
+    public List<String> binaryTreePaths(TreeNode root) {
+        List<String> result = new ArrayList<String>();
+        dfs(root, "", result);
+        return result;
+    }
+    
+    public void dfs(TreeNode node, String str, List<String> result){
+        if(node == null) return;
+        if(str.length() == 0) str = str+node.val;
+        else str = str+"->"+node.val;
+        
+        if(node.left == null && node.right == null) result.add(str);
+        dfs(node.left,str,result);
+        dfs(node.right,str,result);
+    }
+}