问在二进制搜索树中查找对目标值求和的路径

EN

function findsum(tree, target)
  # Traverse the children
  if tree->left
    findsum(tree.left, target)
  if tree->right
    findsum(tree.right, target)

  # Single node forms a valid path
  tree.sums = {tree.value}

  # Add this node to sums of children
  if tree.left
    for left_sum in tree.left.sums
      tree.sums.add(left_sum + tree.value)
  if tree.right
    for right_sum in tree.right.sums
      tree.sums.add(right_sum + tree.value)

  # Have we formed the sum?
  if target in tree.sums
    we have a path

  # Can we form the sum going through this node and both children?
  if tree.left and tree.right
    for left_sum in tree.left.sums
      if target - left_sum in tree.right.sums
        we have a path

  # We no longer need children sums, free their memory
  if tree.left
    delete tree.left.sums
  if tree.right
    delete tree.right.sums

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

    dfsSum(head, sum, currentPath, validPaths);

    return validPaths;
  }

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

    currentPath.add(head.val);

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

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

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

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