描述
给定一个二叉树，找出所有路径中各节点相加总和等于给定目标值的路径。 一个有效的路径，指的是从根节点到叶节点的路径
样例
给定一个二叉树，和 目标值 = 5:
1
/ \
2 4
/ \
2 3
返回：
[
[1, 2, 2],
[1, 4]
]
思路
遍历二叉树，将当前结点值添加到路径，遍历到叶子结点得到每条完整路径，判断路径中各点值是否满足 target，将符合条件路径添加到 result
代码
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root the root of binary tree
* @param target an integer
* @return all valid paths
*/
public List<List<Integer>> binaryTreePathSum(TreeNode root, int target) {
List<List<Integer>> result = new ArrayList<>();
if (root == null) {
return result;
}
ArrayList<Integer> path = new ArrayList<>();
path.add(root.val);
helper(root, path, root.val, target, result);
return result;
}
private void helper(TreeNode root,
ArrayList<Integer> path,
int sum,
int target,
List<List<Integer>> result) {
if (root.left == null && root.right == null) {
if (sum == target) {
result.add(new ArrayList<Integer>(path));
return;
}
}
if (root.left != null) {
path.add(root.left.val);
helper(root.left, path, root.left.val + sum, target, result);
path.remove(path.size() - 1);
}
if (root.right != null) {
path.add(root.right.val);
helper(root.right, path, root.right.val + sum, target, result);
path.remove(path.size() - 1);
}
}
}