leetcode 113. Path Sum II

Question

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]

]

Code

public List<List<Integer>> pathSum(TreeNode root, int sum) {
List<List<Integer>> rst = new ArrayList<>();
List<Integer> solution = new ArrayList<Integer>();

findSum(rst, solution, root, sum);
return rst;
}

private void findSum(List<List<Integer>> result, List<Integer> solution, TreeNode root, int sum) {
if (root == null) {
return;
}

sum -= root.val;

if (root.left == null && root.right == null) {
if (sum == 0) {
solution.add(root.val);
result.add(new ArrayList<Integer>(solution));
solution.remove(solution.size() - 1);
}
return;
}

solution.add(root.val);
findSum(result, solution, root.left, sum);
findSum(result, solution, root.right, sum);
solution.remove(solution.size() - 1);
}