题解 | #二叉树根节点到叶子节点的所有路径和#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    int count = 0;
    /**
     *
     * @param root TreeNode类
     * @return int整型
     */
    public int sumNumbers (TreeNode root) {
        if(root==null) return 0;
        dg(root, new ArrayList<>());
        return count;
    }

    private void dg (TreeNode root, List<Integer> lj) {
        if(root==null) return;

        lj.add(root.val);
        if(root.left==null && root.right==null){ // 叶子节点，计算路径值
            int sum = 0;
            int cj = 1;
            for (int i = lj.size()-1; i >= 0; i--) {
                sum += lj.get(i) * cj;
                cj*=10;
            }
            count += sum;

        }
        if(root.left!=null) dg(root.left, lj); // 遍历左子节点
        if(root.right!=null) dg(root.right, lj); // 遍历右子节点
        lj.remove(lj.size() - 1);
    }
}