路径总和 II

路径总和 II

https://leetcode.cn/problems/path-sum-ii/submissions/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private static List<List<Integer>> listss = new ArrayList<>();

    public void dfs(TreeNode root, int sum, int targetSum, List<Integer> list) {
        if (root==null) {
            return ;
        }
        
        sum += root.val;
        list.add(root.val);
        if (root.left == null && root.right==null) {
            if (sum == targetSum) {
                // listss每次add的list由于是地址的引用，在下面list会remove掉，所以最后的return listss中为[[][]...]
                // 要使用new ArrayLists
                listss.add(new ArrayList<>(list));
            }
        }
        if (root.left!=null) {
            dfs(root.left, sum, targetSum, list);
        }
        
        if (root.right!=null) {
            dfs(root.right, sum, targetSum, list);
        }
        list.remove(list.size()-1);
    }

    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
        listss.clear();
        List<Integer> list = new ArrayList<>();
        int sum = 0;
        dfs(root, sum, targetSum, list);
        return listss;
    }
}