[LintCode] Identical Binary Tree 相同二叉树

Check if two binary trees are identical. Identical means the two binary trees have the same structure and every identical position has the same value.

Have you met this question in a real interview?

 

 

Example

    1             1
   / \           / \
  2   2   and   2   2
 /             /
4             4

are identical.

    1             1
   / \           / \
  2   3   and   2   3
 /               \
4                 4

are not identical.

LeetCode上的原题，请参见我之前的博客Same Tree。

解法一：

class Solution {
public:
    /**
     * @aaram a, b, the root of binary trees.
     * @return true if they are identical, or false.
     */
    bool isIdentical(TreeNode* a, TreeNode* b) {
        if (!a && !b) return true;
        if (!a || !b) return false;
        return a->val == b->val && isIdentical(a->left, b->left) && isIdentical(a->right, b->right);
    }
};

解法二：

class Solution {
public:
    /**
     * @aaram a, b, the root of binary trees.
     * @return true if they are identical, or false.
     */
    bool isIdentical(TreeNode* a, TreeNode* b) {
        stack<TreeNode*> s1, s2;
        if (a) s1.push(a);
        if (b) s2.push(b);
        while (!s1.empty() && !s2.empty()) {
            TreeNode *t1 = s1.top(); s1.pop();
            TreeNode *t2 = s2.top(); s2.pop();
            if (t1->val != t2->val) return false;
            if (t1->left) s1.push(t1->left);
            if (t2->left) s2.push(t2->left);
            if (s1.size() != s2.size()) return false;
            if (t1->right) s1.push(t1->right);
            if (t2->right) s2.push(t2->right);
            if (s1.size() != s2.size()) return false;
        }
        return s1.empty() && s2.empty();
    }
};