L113. Path Sum II

Problem:

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]
]

Solution:

• print all the result

public List<List<Integer>> pathSum(TreeNode root, int sum) {
    List<List<Integer>> res = new ArrayList<>();
    if(root == null) return res;
    List<Integer> list = new ArrayList<>();
    helper(root, sum, res, list);
    return res;
}
private void helper(TreeNode root, int sum, List<List<Integer>> res, List<Integer> list){
    if(root == null) return;
    
    if(root.left == null & root.right == null){
        if(sum == root.val){
            list.add(root.val);
            res.add(new ArrayList<>(list));
            list.remove(list.size()-1);
            return;
        }
    }
    list.add(root.val);
    helper(root.left, sum - root.val, res, list);
    helper(root.right, sum - root.val, res, list);
    list.remove(list.size()-1);
}