思路:题目需要记录从根节点开始走的路径,无疑选用前序遍历,用一个数组paths 记录走过的节点信息,遇到叶子节点就用另一个list记录下路径,回溯时删掉paths尾节点即可
class Solution {public List<String> binaryTreePaths(TreeNode root) {List<String> list = new ArrayList<>(); //处理的结果if(root == null) {return list;}List<Integer> paths = new ArrayList<>(); //当前路径顺序func(root, paths, list);return list;}public void func(TreeNode root, List<Integer> paths, List<String> list) {//前序遍历,中paths.add(root.val);//如果是叶子节点,就记录下路径if(root.left==null && root.right == null) {StringBuilder sb = new StringBuilder();for (int i = 0; i < paths.size()-1; i++) {sb.append(paths.get(i)).append("->");}sb.append(paths.get(paths.size()-1));list.add(sb.toString());//return;}//左,不是叶子节点就一直递归深入if(root.left != null) {func(root.left, paths, list);paths.remove(paths.size()-1);//结束一轮递归要回退一步}//右if(root.right != null) {func(root.right, paths, list);paths.remove(paths.size()-1);}}}