Same Tree

最新推荐文章于 2023-11-01 20:19:49 发布

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#leetcode Same Tree #递归 #bfs #dfs

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本文介绍三种方法来判断两个二叉树是否结构相同且节点值相等：深度优先搜索递归同步遍历、非递归深度优先搜索遍历、广度优先搜索遍历。每种方法都确保考虑了空节点，从而准确比较树结构。

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.

解法1： DFS递归同步遍历两棵树
解法2：用栈来实现非递归DFS遍历两棵树
解法3：用queue来实现BFS遍历比较两棵树

解法2，3能够有效是因为把每个节点的null节点也当作遍历比较的一部分，这样就避免了结构不同但是单个遍历结果相同的错误。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isSameTree(TreeNode *p, TreeNode *q) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        
        // 1
        if (p == NULL || q == NULL) return p == q;
        if (p->val != q->val) return false;
        return isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
        
        // 2
        /*
        stack<TreeNode*> pt, qt;
        pt.push(p);
        qt.push(q);
        while (!pt.empty() && !qt.empty()) {
            TreeNode *pnode = pt.top();
            pt.pop();
            TreeNode *qnode = qt.top();
            qt.pop();
            if (pnode == NULL || qnode == NULL) {
                if (pnode != qnode) return false;
                continue;
            }
            
            if (pnode->val != qnode->val) return false;
            pt.push(pnode->left);
            pt.push(pnode->right);
            qt.push(qnode->left);
            qt.push(qnode->right);
        }
        
        return pt.empty() && qt.empty();
        */
        
        // 3
        /*
        queue<TreeNode*> quep, queq;
        quep.push(p);
        queq.push(q);
        while (!quep.empty() && !queq.empty()) {
            TreeNode *pnode = quep.front();
            quep.pop();
            TreeNode *qnode = queq.front();
            queq.pop();
            if (pnode == NULL || qnode == NULL) {
                if (pnode != qnode) return false;
                continue;
            }
            
            if (pnode->val != qnode->val) return false;
            quep.push(pnode->left);
            quep.push(pnode->right);
            queq.push(qnode->left);
            queq.push(qnode->right);
        }
        
        return quep.empty() && queq.empty();
        */
    }
};