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leetcode257. binary tree paths

admin 11月 13, 2020 0

获得二叉树的所有路径，代码非常简洁。

257. Binary Tree Paths

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

For example, given the following binary tree:

1
2
3
4
5
 
   1
 /   
2     3
 
  5

All root-to-leaf paths are:

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

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

算法：基于深度优先遍历算法，遇到叶子节点就将当前路径加入结果集合。

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public List<String> (TreeNode root) {
    List<String> ans = new ArrayList<>();
    if (root != null) preorderWalk(root, "", ans);
    return ans;
}
public void preorderWalk(TreeNode root, String path, List<String> ans) {
    if (root.left == null && root.right == null) ans.add(path + root.val);
    if (root.left != null) preorderWalk(root.left, path + root.val + "->", ans);
    if (root.right != null) preorderWalk(root.right, path + root.val + "->", ans);
}
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