https://www.nowcoder.com/practice/6e196c44c7004d15b1610b9afca8bd88

递归

涉及到树的问题一般都要递归做，第一次做没啥思路，代码参考自《剑指offer》层次稍微清晰一点。

  1. public boolean HasSubtree(TreeNode root1, TreeNode root2) {
  2.     boolean result = false;
  3.     if (root1 != null && root2 != null) {
  4.         if (root1.val == root2.val) {
  5.             result = HasSubtreeCore(root1, root2);
  6.         }
  7.         if (!result)
  8.             result = HasSubtree(root1.left, root2);
  9.         if (!result)
  10.             result = HasSubtree(root1.right, root2);
  11.     }
  12.     return result;
  13. }
  15. public boolean HasSubtreeCore(TreeNode root1, TreeNode root2) {
  16.     if (root2 == null)
  17.         return true;
  18.     if (root1 == null)
  19.         return false;
  20.     if (root1.val != root2.val)
  21.         return false;
  23.     return HasSubtreeCore(root1.left, root2.left) && HasSubtreeCore(root1.right, root2.right);
  24. }