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题目： 

 

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解析： 

 

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代码： 

private List<String> ret = new ArrayList<>();public List<String> binaryTreePaths(TreeNode root) {dfs(root,new StringBuffer());return ret;}private void dfs(TreeNode root, StringBuffer no_path){//把path设置为局部变量，让函数帮我们 “恢复现场”StringBuffer path = new StringBuffer(no_path);path.append(Integer.toString(root.val));//叶子节点        if(root.left == null && root.right == null){ret.add(path.toString());return;}//非叶子节点path.append("->");//加上剪枝写法if(root.left != null) dfs(root.left,path);if(root.right != null) dfs(root.right,path);}