113. 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:

Simple backtracking.

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} sum
 * @return {number[][]}
 */
let pathSum = function (root, sum, path = [], result = []) {
  if (!root) {
    return result;
  }

  if (root.left === null && root.right === null) {
    if (root.val === sum) {
      result.push([...path, root.val]);
    }
    return result;
  }

  path.push(root.val);
  pathSum(root.left, sum - root.val, path, result);
  pathSum(root.right, sum - root.val, path, result);
  path.pop();

  return result;
};

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