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LeetCode 113.Path Sum II

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Question

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

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

Explanation

递归的时候保留路径，满足就存入全局变量中。

Code

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private List<List<Integer>> resultList = new ArrayList<List<Integer>>();
    public void pathSumHelper(TreeNode root, int sum, ArrayList<Integer> path){
        path.add(root.val);
        if (root == null) return;
        if (root.left == null && root.right == null) {
            if (root.val== sum) {
                resultList.add(new ArrayList<Integer>(path));
            }
        }
        if (root.left != null) pathSumHelper(root.left, sum - root.val, path);
        if (root.right != null) pathSumHelper(root.right, sum - root.val, path);
        path.remove(path.size()-1);
    }
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        if(root==null) return resultList;
        ArrayList<Integer> path = new ArrayList<>();
        pathSumHelper(root, sum, path);
        return resultList;
    }
}