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Leetcode113-pathSumII

Posted on Edited on In Views: Valine:
Solution Report of LeetCode Acceptted

Description

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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2
3
4
5
6
7
      5
     / \
    4   8
   /   / \
  11  13  4
 /  \    / \
7    2  5   1

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

Solution

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> res = new ArrayList<>();
        if (root == null) return res;
        helper(root, sum, res, new ArrayList<Integer>(), 0);
        return res;
    }
    
    private void helper(TreeNode node, int target, List<List<Integer>> res, List<Integer> cur, int sum){
        cur.add(node.val);
        sum += node.val;
        if (node.left == null && node.right == null && sum == target){
            res.add(new ArrayList<>(cur));
            return;
        }
        // System.out.println(cur + ", " + sum);
        if (node.left != null){
            helper(node.left, target, res, cur, sum);
            cur.remove(cur.size()-1);
        }
        if (node.right != null){
            helper(node.right, target, res, cur, sum);
            cur.remove(cur.size()-1);
        }
    }
}