二叉树之路径系列

节点定义

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;
    }
    @Override
    public String toString() {
        return String.valueOf(this.val);
    }
}

根节点到所有叶子节点的路径

    public static void main(String[] args){
        TreeNode root=new TreeNode(1); 
        List<String>paths=new ArrayList<>();
        getPath(root,paths,root.val+"");
    }

    //记录根节点到叶子结点的所有路径
    public static void getPath(TreeNode node, List<String> paths,String s){
        if(node.left==null&&node.right==null){ //叶子结点
            paths.add(s);
            return;
        }
        if(node.left!=null){
            getPath(node.left, paths, s);
        }
        if(node.right!=null){
            getPath(node.right, paths, s);
        }
    }

根节点到指定节点的路径

//寻找根节点到某一特定子节点路径
    public static boolean getPathToNode(TreeNode node, List<Integer> path, int target) {
        path.add(node.val);
        if (node.val == target) return true;
        boolean flag = false;
        if (node.left != null) {
            flag = getPathToNode(node.left, path, target);
        }
        if (!flag&&node.right != null) {
            flag = getPathToNode(node.right, path, target);
        }
        //当前节点及其子树 都未找到target 需要在返回父节点之前，在路径上删除当前节点(回溯)
        if (!flag) path.remove(path.size() - 1);
        return flag;
    }

参考链接：

https://blog.csdn.net/liuyi1207164339/article/details/50908308

https://blog.csdn.net/better_xf/article/details/79856447