輸入一棵二叉樹和一個整數,打印出二叉樹中節點值的和爲輸入整數的所有路徑。從樹的根節點開始往下一直到葉節點所經過的節點形成一條路徑。
示例:
給定如下二叉樹,以及目標和 sum = 22,
5
/ \
4 8
/ / \
11 13 4
/ \ / \
7 2 5 1
返回:
[
[5,4,11,2],
[5,8,4,5]
]
提示:
節點總數 <= 10000
題解:
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
List<List<Integer>> res = new ArrayList();
public List<List<Integer>> pathSum(TreeNode root, int sum) {
traceSum(root, sum, new ArrayList());
return res;
}
private void traceSum(TreeNode node, int target, List<Integer> collector) {
if(node == null) return;
collector.add(node.val);
target -= node.val;
if(target == 0 && node.left == null && node.right == null) {
res.add(new ArrayList(collector));
} else {
traceSum(node.left, target, collector);
traceSum(node.right, target, collector);
}
//回溯 後退,因爲整個過程用的同一個收集器
collector.remove(collector.size() - 1);
}
}