Question:

You are given a binary tree in which each node contains an integer value.

Find the number of paths that sum to a given value.

The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).

The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.

Example:

root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8

      10
     /  \
    5   -3
   / \    \
  3   2   11
 / \   \
3  -2   1

Return 3. The paths that sum to 8 are:

1.  5 -> 3
2.  5 -> 2 -> 1
3. -3 -> 11

Solution:

  • Method 1: dfs + bfs ```Java /**
    • Definition for a binary tree node.
    • public class TreeNode {
    • int val;
    • TreeNode left;
    • TreeNode right;
    • TreeNode(int x) { val = x; }
    • } */ class Solution { private int result; public int pathSum(TreeNode root, int sum) { if(root == null) return 0; Queue q = new LinkedList<>(); q.offer(root); while(!q.isEmpty()){ TreeNode node = q.poll(); dfs(node, 0, sum); if(node.left != null) q.offer(node.left); if(node.right != null) q.offer(node.right); } return result; } private void dfs(TreeNode node, int cur, int sum){ if(node == null) return; if(cur + node.val == sum) result++; dfs(node.left, cur + node.val, sum); dfs(node.right, cur + node.val, sum); } } ```