【leetcode】113. Path Sum II【java】

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
For 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]
]

回溯法
/**
* 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<List<Integer>> pathSum(TreeNode root, int sum) {
List<List<Integer>> result = new ArrayList<>();
List<Integer> solution = new ArrayList<>();
backTrack(result, solution, root, sum);
return result;
}
public void backTrack(List<List<Integer>> result, List<Integer> solution, TreeNode root, int sum){
if (root == null){
return;
}
solution.add(root.val);
if (root.left == null && root.right == null && root.val == sum){
result.add(new ArrayList(solution));
} else {
backTrack(result, solution, root.left, sum - root.val);
backTrack(result, solution, root.right, sum - root.val);
}
solution.remove(solution.size() - 1);
}
}