p257

LeetCode p257 Binary Tree Paths 题解

1.题目：

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”]

题意：

输出一个二叉树包含的所有的路径。

2.解题思路:

见代码

3.代码

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[title] [] [url] [link text]

 
/**
 * 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> ans = new ArrayList<String>();

	public List<String> binaryTreePaths(TreeNode root) {
		List<Integer> list = new ArrayList<Integer>();
		binaryTreePaths(root, list);
		return ans;
	}

	public void binaryTreePaths(TreeNode root, List<Integer> list) {
		if (root == null)
			return;
		if (root.left == null && root.right == null) {
			list.add(root.val);
			int len = list.size();
			StringBuilder builder = new StringBuilder();
			for (int i = 0; i < len - 1; i++) {
				builder.append(list.get(i) + "->");
			}
			builder.append(list.get(len - 1));
			// System.out.println(sb.toString());
			ans.add(builder.toString());
			// sb.deleteCharAt(sb.length() - 1);
			return;
		}
		list.add(root.val);
		if (root.left != null) {
			binaryTreePaths(root.left, list);
			list.remove(list.size() - 1);
		}

		if (root.right != null) {
			binaryTreePaths(root.right, list);
			list.remove(list.size() - 1);
		}

	}
}

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4.一些总结：