題目：

Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

   1
 /   \
2     3
 \
  5

All root-to-leaf paths are:

["1->2->5", "1->3"]

用深度優先遍歷，類似二叉樹的前序變遍歷

程式碼：

public class LeetCode257_BinaryTreePaths {
	 static List<String> paths=new ArrayList<>();
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TreeNode p1=new TreeNode(1);
		TreeNode p2=new TreeNode(2);
//		TreeNode p3=new TreeNode(3);
//		TreeNode p4=new TreeNode(5);
		p1.left=p2;
//		p1.right=p3;
//		p2.left=p4;
		
		binaryTreePaths(p1);

	}
	
	 public static  List<String> binaryTreePaths(TreeNode root) {
		
		 if(root==null)
			 return paths;
		 String curPath="";
		 serachTree(root, curPath);
		 return paths;
		 
		 
		
	    }
	 
	 public static void serachTree(TreeNode root,String currentPath) {
		 
		 currentPath+=root.val;
		 if(root.left==null&&root.right==null)
		 {
			 paths.add(currentPath);
			 System.out.println(currentPath);
			 return;
		 }
		 currentPath+="->";
		 if(root.left!=null)
			 serachTree(root.left, currentPath);
		 if(root.right!=null)
			 serachTree(root.right, currentPath);
		
	}
	 
	 

}