二叉树（BT）相关

1.same tree　　

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
  public class Solution {
      public boolean isSameTree(TreeNode p, TreeNode q) {      
          if(p==null && q==null)
              return true;
          if(p==null || q==null)
              return false;
          if(p.val!=q.val)
              return false;
          return isSameTree(p.left, q.left)&&isSameTree(p.right, q.right);
      }     
  }

2.symmetric-tree(mirror-tree)（对称树）

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public static boolean isSymmetric(TreeNode root) {
        if(root==null)
            return true;
        return isMirror(root.left, root.right);
    }
    
    public static boolean isMirror(TreeNode p,TreeNode q) {
        if(p==null && q==null)
            return true;
        if(p==null || q==null)
            return false;
        if(p.val!=q.val)
            return false;
        return isMirror(p.left, q.right)&&isMirror(p.right, q.left);
    }
    
}