Tree——No.100 Same Tree

Problem：

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Explanation：

判断两棵树是否相等。

My Thinking：

使用递归

My Solution：

class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if(p==null && q==null)//两结点都为空
            return true;
        if(p==null || q==null)//两结点有一个为空，则一定不相等
            return false;
        if(p.val!=q.val){//两结点都非空，值不等
            return false;
        }else{
            return isSameTree(p.left,q.left) && isSameTree(p.right,q.right);
        }
    }
}

Optimum Thinking:

1. 同my thinking
2. 使用栈

Optimum Solution：

（2）

class Solution {
    public boolean check(TreeNode p, TreeNode q) {
        if (p == null && q == null) return true;
        if (q == null || p == null) return false;
        if (p.val != q.val) return false;
        return true;
  }
    public boolean isSameTree(TreeNode p, TreeNode q) {
//检查根结点
        if (p == null && q == null) return true;
        if (!check(p, q)) return false;

        ArrayDeque<TreeNode> deqP = new ArrayDeque<TreeNode>();
        ArrayDeque<TreeNode> deqQ = new ArrayDeque<TreeNode>();
        deqP.addLast(p);
        deqQ.addLast(q);

        while (!deqP.isEmpty()) {
          p = deqP.removeFirst();
          q = deqQ.removeFirst();

          if (!check(p, q)) return false;
          if (p != null) {
            // in Java nulls are not allowed in Deque
            if (!check(p.left, q.left)) return false;
            if (p.left != null) {
              deqP.addLast(p.left);
              deqQ.addLast(q.left);
            }
            if (!check(p.right, q.right)) return false;
            if (p.right != null) {
              deqP.addLast(p.right);
              deqQ.addLast(q.right);
            }
          }
        }
        return true;
    }
}