Same Tree (JAVA实现)

来源：互联网发布：linux更改文件权限777 编辑：程序博客网时间：2024/06/05 20:59

原题再现：

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

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

翻译：给定两个二叉树，判断是否相等，当结构相同且树节点有相同值。

算法一：

递归：

<span style="font-size:18px;">public boolean isSameTree(TreeNode p, TreeNode q) {        if(p == null && q == null) return true;        if(p == null || q == null || p.val != q.val) return false;        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);    }</span>

深层次来说，一句话也可以将其实现：

public boolean isSameTree(TreeNode p, TreeNode q) {    return (p == null || q == null) ? p == q : p.val == q.val &&        isSameTree(p.left, q.left) && isSameTree(p.right, q.right);}

算法二：

利用栈的思想：

（1）只利用一个栈就可以实现：

<span style="font-size:18px;">public boolean isSameTree(TreeNode p, TreeNode q) {        Stack<TreeNode> stack = new Stack<TreeNode>();        stack.push(q);        stack.push(p);        while(!stack.isEmpty()){            TreeNode pn = stack.pop();            TreeNode qn = stack.pop();            if(pn == null && qn == null){                continue;            }else if(pn == null || qn == null){                return false;            }else if(pn.val != qn.val){                return false;            }            stack.push(pn.right);            stack.push(qn.right);            stack.push(pn.left);            stack.push(qn.left);                    }        return true;    }</span>

（2）利用双栈也可以实现：

<span style="font-size:18px;">public boolean isSameTree(TreeNode p, TreeNode q) {     Stack<TreeNode> stack_p = new Stack <> ();            Stack<TreeNode> stack_q = new Stack <> ();     if (p != null) stack_p.push( p ) ;     if (q != null) stack_q.push( q ) ;     while (!stack_p.isEmpty() && !stack_q.isEmpty()) {     TreeNode pn = stack_p.pop() ;     TreeNode qn = stack_q.pop() ;         if (pn.val != qn.val) return false ;     if (pn.right != null) stack_p.push(pn.right) ;     if (qn.right != null) stack_q.push(qn.right) ;     if (stack_p.size() != stack_q.size()) return false ;     if (pn.left != null) stack_p.push(pn.left) ;               if (qn.left != null) stack_q.push(qn.left) ;     if (stack_p.size() != stack_q.size()) return false ;     }          return stack_p.size() == stack_q.size() ;  }</span>

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