[LeetCode] Same Tree

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.

思路一：前序递归的思想。时间复杂度O(n),空间复杂度O(logN)

　　

/**
 * 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) {
        if (!p && !q) return true;
        if (!p || !q ) return false;
        
        return (p->val == q->val) && isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
    }
};

思路二：层次遍历的思想。时间复杂度O(n), 空间复杂度O(logN)

　　

/**
 * 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) {
        queue<TreeNode *> s;
        s.push(p);
        s.push(q);
        
        while (!s.empty()) {
            p = s.front();
            s.pop();
            q = s.front();
            s.pop();
            if (!p && !q) continue;
            if (!p || !q) return false;
            if (p->val != q->val) return false;
            
            s.push(p->left);
            s.push(q->left);
            s.push(p->right);
            s.push(q->right);
        }
        
        return true;
    }
};