原题链接:https://leetcode.com/problems/path-sum-ii/
Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
Note: A leaf is a node with no children.
Example:
Given the below binary tree and sum = 22
,
5 / \ 4 8 / / \ 11 13 4 / \ / \ 7 2 5 1
Return:
[ [5,4,11,2], [5,8,4,5] ]
思路:递归回溯。
AC 1ms 99.6% Java:
/**
* 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>> ans=new ArrayList();
public List<List<Integer>> pathSum(TreeNode root, int sum) {
if(root==null)
return ans;
helper(root,sum,new ArrayList<Integer>());
return ans;
}
public void helper(TreeNode root,int sum,List<Integer> list){
if(root==null)
return;
int remain=sum-root.val;
list.add(root.val);
if(remain==0&&root.left==null&&root.right==null){
ans.add(new ArrayList(list));
}
helper(root.left,remain,list);
helper(root.right,remain,list);
list.remove(list.size()-1);
}
}