题解 | #二叉树根节点到叶子节点的所有路径和#回溯算法

import java.util.*;

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

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return int整型
     */
    public static ArrayList<LinkedList<Integer>> res = new ArrayList<>();
    public int sumNumbers (TreeNode root) {
        if(root == null) return 0;
        LinkedList<Integer> ll = new LinkedList<Integer>();
        ll.add(root.val);
        printTree(root,ll);
        int finalresult = 0;
        for(int i = 0;i<res.size();i++){
            LinkedList<Integer> lres = res.get(i);
            int lsum = 0;
            while(!lres.isEmpty()){
                lsum = lsum *10 + lres.removeFirst();
            }
            finalresult += lsum;
        }
        return finalresult;
    }
    public static void printTree(TreeNode node,LinkedList<Integer> ll){
        if(node.left == null && node.right == null){
            LinkedList<Integer> lres = new LinkedList<>();
            for(Integer x:ll){
                lres.add(x);
            }
            res.add(lres);
            System.out.println(lres.toString());
            return;
        }
        if(node.left != null){
            ll.add(node.left.val);
            printTree( node.left, ll);
            ll.removeLast();
        }
        if(node.right !=null){
            ll.add(node.right.val);
            printTree( node.right, ll);
            ll.removeLast();
        }
    }
}