《LeetCode力扣练习》代码随想录——二叉树（二叉树的所有路径—Java）

刷题思路来源于 代码随想录

257. 二叉树的所有路径

• 二叉树-前序遍历

  /**
   * Definition for a binary tree node.
   * public 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;
   * }
   * }
   */
  class Solution {
      public List<String> binaryTreePaths(TreeNode root) {
  
          List<String> result = new ArrayList<>();
  
          if (root == null) {
              return result;
          }
  
          List<Integer> path = new ArrayList<>();
          recursion(root, path, result);
  
          return result;
  
      }
  
      private void recursion(TreeNode root, List<Integer> path, List<String> result) {
  
          path.add(root.val);
  
          if (root.left == null && root.right == null) {
  
              StringBuilder sb = new StringBuilder();
              for (int i = 0; i < path.size() - 1; i++) {
  
                  sb.append(path.get(i)).append("->");
  
              }
  
              sb.append(path.get(path.size() - 1));
              result.add(sb.toString());
              return;
  
          }
  
          if (root.left != null) {
  
              recursion(root.left, path, result);
              path.remove(path.size() - 1);
  
          }
  
          if (root.right != null) {
  
              recursion(root.right, path, result);
              path.remove(path.size() - 1);
  
          }
  
      }
  }