Leetcode Binary Tree Paths

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"]

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解题思路：

依然recursion! 用DFS。 关键点：让路径string 伴随着遍历树的点，点到哪里，路径值跟到哪里。

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Java code:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<String> binaryTreePaths(TreeNode root) {
        List<String> result = new ArrayList<String>();
        if(root == null) { return result; }
        String path = root.val + "";
        getPath(root, result, path);
        return result;
    }
    
    void getPath(TreeNode root, List<String> result, String path) {
        if(root.left == null && root.right == null) {
            result.add(path);
        }
        if(root.left != null) {
            getPath(root.left, result, path+"->"+root.left.val+"");
        }
        if(root.right != null) {
            getPath(root.right, result, path+"->"+root.right.val+"");
        }
    }
}

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Reference:

1. http://www.hihuyue.com/hihuyue/codepractise/leetcode/leetcode174-binary-tree-paths