[LeetCode] Problem 113 - Path Sum II

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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,

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7
      5
     / \
    4   8
   /   / \
  11  13  4
 /  \    / \
7    2  5   1

Return:

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[
   [5,4,11,2],
   [5,8,4,5]
]

Code

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public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}
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public List<List<Integer>> pathSum(TreeNode root, int sum) {
    List<List<Integer>> result = new ArrayList<>();

    pathSumHelper(result, new ArrayList<>(), root, sum);

    return result;
}

private void pathSumHelper(List<List<Integer>> result, List<Integer> path, TreeNode root, int sum) {
    if (root == null)
        return;
    
    path.add(root.val);

    if (root.left == null && root.right == null) {
        if (root.val == sum)
            result.add(new ArrayList<>(path));
    }

    pathSumHelper(result, path, root.left, sum - root.val);
    pathSumHelper(result, path, root.right, sum - root.val);
    path.remove(path.size() - 1);
}