Leetcode 257. Binary Tree Path

Question

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"]

Explanation

分治法，只用考虑左右子树会出现的情况就好了。另外此处注意叶子节点，就不用加“->”了。

Code

public class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> result = new ArrayList<>();
        if (root == null) return result;
        if (root.left == null && root.right == null) result.add(Integer.toString(root.val));
        List<String> left = binaryTreePaths(root.left);
        List<String> right = binaryTreePaths(root.right);
        for(String s:left) {
            result.add(root.val+"->"+s);
        }
        for(String s: right) {
            result.add(root.val + "->" + s);
        }
        return result;
    }
}