LeetCode(53)-Binary Tree Paths
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"]
思路:
- 题意:求二叉树根到叶子的所有路径
- 二叉树的问题,没有一次递归解决不了的,如果有,那就两次,判断左右子树,都为空是叶子节点,否则一直递归下去,然后传入List参数和ArrayList参数
-
代码:
public class Solution {
public List<String> binaryTreePaths(TreeNode root) {
List<String> all = new ArrayList<String>();
if(root == null){
return all;
}
getTreePaths(all,new ArrayList<Integer>(),root);
return all;
}
private void getTreePaths(List<String> result,List<Integer> tmp,TreeNode node){
if(node == null){
return;
}else{
tmp.add(node.val);
}
if(node.left == null && node.right == null){
result.add(getString(tmp));
}
if(node.left != null){
getTreePaths(result,new ArrayList(tmp),node.left);
}
if(node.right != null){
getTreePaths(result,new ArrayList(tmp),node.right);
}
}
private String getString(List<Integer> tmp){
StringBuffer sb= new StringBuffer();
if(tmp == null||tmp.isEmpty()){
return null;
}
sb.append(tmp.get(0));
for(int i = 1;i < tmp.size();i++){
sb.append("->").append(tmp.get(i));
}
return sb.toString();
}
}
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