【剑指Offer】34. 二叉树中和为某一值的路径

import java.util.ArrayList;
/**
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
public class Solution {

    private ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
    
    public ArrayList<ArrayList<Integer>> FindPath(TreeNode root,int target) {
        backtracking(root, target, new ArrayList<Integer>());
        return ret;
    }
    
    // 等值的路径和
    private void backtracking(TreeNode root, int target, ArrayList<Integer> path) {
        if(root == null)
            return;
        target -= root.val;
        path.add(root.val);
        
        if(target==0 && root.left == null && root.right == null)
            ret.add(new ArrayList<>(path));
        else {
            backtracking(root.left, target, path);
            backtracking(root.right, target, path);
        }
        path.remove(path.size()-1);
    }
}