257. 二叉树的所有路径

257. 二叉树的所有路径

原题

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private List<String> ans = new ArrayList<>();
    public List<String> binaryTreePaths(TreeNode root) {
        if(root==null){
            return ans;
        }
        dfs(root,"");
        return ans;
    }

    public void dfs(TreeNode node,String str){
        //为叶子结点
        if(node.left==null&&node.right==null){
             str =  str + node.val;
             ans.add(str);
             return;
        }
        str =  str + node.val + "->" ;
        //遍历左子树
        if(node.left!=null){
            dfs(node.left,str);
        }
        //遍历右子树
        if(node.right!=null){
            dfs(node.right,str);
        }
        

    }
}
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