Find paths in a binary search tree summing to a target value

Question

Given a binary search tree and a target value, find all the paths (if there exists more than one) which sum up to the target value. It can be any path in the tree. It doesn\'t h

Answer 1

Old question, but here's my stab at it - should be O(n) time as your visiting each node only once:

  public static List> pathSum(Node head, int sum) {
    List currentPath = new ArrayList();
    List> validPaths = new ArrayList>();

    dfsSum(head, sum, currentPath, validPaths);

    return validPaths;
  }

  public static void dfsSum(Node head, int sum, List currentPath, List> validPaths) {
    if (head == null) return;

    currentPath.add(head.val);

    if (head.left == null && head.right == null && sum == head.val) {
      validPaths.add(new ArrayList(currentPath));
    }

    dfsSum(head.left, sum - head.val, new ArrayList(currentPath), validPaths);
    dfsSum(head.right, sum - head.val, new ArrayList(currentPath), validPaths);
  }

And the node class:

class Node {
    public int val;
    public Node left;
    public Node right;

    public Node(int val) {
      this.val = val;
    }
  }