# 38. 二叉树的所有路径

java

```java
public class TreeNode {
    public int val;
    public TreeNode left;
    public TreeNode right;

    public TreeNode(int x) {
        val = x;
    }

}


public class TreeUtils {

    public static int k=0;

    public static int k2=0;

    public static TreeNode stringToTree(String s){
        k=0;
        TreeNode root=null;
        root=createTree(root,s);
        return root;
    }

    private static TreeNode createTree(TreeNode node,String s){
        char ch=s.charAt(k++);
        if(ch=='#') return null;
        else{
            node=new TreeNode(ch-'0');
            node.left=createTree(node.left,s);
            node.right=createTree(node.right,s);
            return node;
        }
    }

    public static TreeNode stringToTreeWith(String str,String separator){
        k2=0;
        TreeNode root=null;
        String[] arr=str.trim().split(separator);
        root=createTreeWith(root,arr);
        return root;
    }

    private static TreeNode createTreeWith(TreeNode node,String[] arr){
        String v=arr[k2++];
        if(v.equals("#")) return null;
        else{
            node=new TreeNode(Integer.valueOf(v));
            node.left=createTreeWith(node.left,arr);
            node.right=createTreeWith(node.right,arr);
            return node;
        }
    }

    /**
     * 先序遍历
     * @param root
     */
    public static void travser(TreeNode root){
        if(root!=null){
            System.out.print(root.val+" ");
            travser(root.left);
            travser(root.right);
        }
    }

    /**
     * 中序遍历
     * @param root
     */
    public static void travser2(TreeNode root){
        if(root!=null){
            travser2(root.left);
            System.out.print(root.val+" ");
            travser2(root.right);
        }
    }

    /**
     * 后序遍历
     * @param root
     */
    public static void travser3(TreeNode root){
        if(root!=null){
            travser3(root.left);
            travser3(root.right);
            System.out.print(root.val+" ");
        }
    }
}



/**
 * 257. 二叉树的所有路径
 *
 * 给定一个二叉树，返回所有从根节点到叶子节点的路径。
 *
 * 说明: 叶子节点是指没有子节点的节点。
 *
 * 示例:
 *
 * 输入:
 *
 *    1
 *  /   \
 * 2     3
 *  \
 *   5
 *
 * 输出: ["1->2->5", "1->3"]
 *
 * 解释: 所有根节点到叶子节点的路径为: 1->2->5, 1->3s
 */

import java.util.ArrayList;
import java.util.List;
public class Solution257 {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> list=new ArrayList<>();
        todo(root,list,"");
        return list;
    }

    public void todo(TreeNode root,List<String> list,String s) {
        String tmp=(s.length()==0?"":s+"->");
        if(root!=null){
            if(root.left==null&&root.right==null) {
                list.add(tmp+root.val);
            }else{
                todo(root.left,list,tmp+root.val);
                todo(root.right,list,tmp+root.val);
            }
        }
    }

    public static void main(String[] args){
        TreeNode root=TreeUtils.stringToTree("12#5##3##");
        List<String> r=new Solution257().binaryTreePaths(root);
        for(String s:r){
            System.out.println(s);
        }
    }
}
```


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