113. Path Sum II

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LeetCode

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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]
]

Code

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    List<List<Integer>> res;
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        res = new ArrayList<>();

        helper(root, sum, new ArrayList<>());

        return res;
    }

    private void helper(TreeNode root, int sum, List<Integer> temp){
        if(root == null) return;
        if(root.left == null && root.right == null){
            if(root.val == sum){
                temp.add(root.val);
                res.add(new ArrayList<>(temp));
                // 清除这个path
                temp.remove(temp.size() - 1);
            }

            return;
        }

        temp.add(root.val);
        helper(root.left, sum - root.val, temp);
        helper(root.right, sum - root.val, temp);
        temp.remove(temp.size() - 1);
    }
}