100. Same Tree

題目原文

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

解題思路

1. 先從兩棵樹的左子樹開始追蹤，追蹤到兩邊都是葉子節點則返回True。

2. 再檢查右子樹，兩邊都是葉子節點，則返回True。

3. 如果遇到一邊是葉子節點，另一邊還有兒子，則返回False。

4. 或者是兩邊的值不一樣，則返回False。

程式解答

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