剑指offer:面试题25、二叉树中和为某值的路径

题目描述

输入一颗二叉树的根节点和一个整数，按字典序打印出二叉树中结点值的和为输入整数的所有路径。路径定义为从树的根结点开始往下一直到叶结点所经过的结点形成一条路径。

代码示例

import java.util.ArrayList;
import java.util.List;

public class Offer25 {
    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(3);
        root.left.left = new TreeNode(1);
        Offer25 testObj = new Offer25();
        List<List<Integer>> ret = testObj.findPath(root, 4);
        for (List<Integer> list: ret) {
            System.out.println(list);
        }
    }

    static class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int val) {
            this.val = val;
        }
    }

    private List<List<Integer>> ret = new ArrayList<>();

    public List<List<Integer>> findPath(TreeNode root, int target) {
        backtracking(root, target, new ArrayList<>());
        return ret;
    }

    private void backtracking(TreeNode node, int target, List<Integer> path) {
        if (node == null)
            return;
        path.add(node.val);
        target -= node.val;
        if (target == 0 && node.left == null && node.right == null) {
            ret.add(new ArrayList<>(path));
        } else {
            backtracking(node.left, target, path);
            backtracking(node.right, target, path);
        }
        path.remove(path.size() - 1);
    }
}