100.same-tree.cpp

/*
 * @lc app=leetcode id=100 lang=cpp
 *
 * [100] Same Tree
 *
 * https://leetcode.com/problems/same-tree/description/
 *
 * algorithms
 * Easy (49.40%)
 * Total Accepted:    351.6K
 * Total Submissions: 711K
 * Testcase Example:  '[1,2,3]\n[1,2,3]'
 *
 * 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.
 *
 * Example 1:
 *
 *
 * Input:     1         1
 * ⁠         / \       / \
 * ⁠        2   3     2   3
 *
 * ⁠       [1,2,3],   [1,2,3]
 *
 * Output: true
 *
 *
 * Example 2:
 *
 *
 * Input:     1         1
 * ⁠         /           \
 * ⁠        2             2
 *
 * ⁠       [1,2],     [1,null,2]
 *
 * Output: false
 *
 *
 * Example 3:
 *
 *
 * Input:     1         1
 * ⁠         / \       / \
 * ⁠        2   1     1   2
 *
 * ⁠       [1,2,1],   [1,1,2]
 *
 * Output: false
 *
 *
 */
/**
 * Definition for a binary tree node.
 * 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) {
        // 不用嵌套if，其实就4种情况
        if (!p && !q) {
            // 都是nullptr
            return true;
        }
        if (!p || !q) {
            // 其中有一个是nullptr
            return false;
        }
        // 都不是nullptr
        return p->val == q->val && isSameTree(p->left, q->left) && isSameTree(p->right, q->right);
    }
};