[LeetCode]--257. 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”]
Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

这种第一时间想到的就是递归啦。考虑好结束条件，就是左右子树都为空即叶子节点为结束条件，依次递归，不过要考虑好字符串的处理问题。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    List<String> result = new LinkedList<String>();
    List<Integer> path = new LinkedList<Integer>();
    public List<String> binaryTreePaths(TreeNode root) {
        if(root ==null) return result;
        getPaths(root);
        return result;
    }
    public void getPaths(TreeNode node){
        if(node == null) return;
        path.add(node.val);
        if(node.left == null && node.right == null){
            StringBuffer buffer = new StringBuffer();
            for(int i=0;i<path.size();i++){
                if(i!=0)
                    buffer.append("->");
                buffer.append(path.get(i));
            }
            result.add(buffer.toString());
        }
        getPaths(node.left);
        getPaths(node.right);
        path.remove(path.size()-1);
    }
}