[LintCode] 翻转二叉树

递归实现：

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    void invertBinaryTree(TreeNode *root) {
        // write your code here
        if (!root) return;
        swap(root -> left, root -> right);
        invertBinaryTree(root -> left);
        invertBinaryTree(root -> right);
    }
};

迭代实现：

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param root: a TreeNode, the root of the binary tree
     * @return: nothing
     */
    void invertBinaryTree(TreeNode *root) {
        // write your code here
        if (!root) return;
        queue<TreeNode*> level;
        level.push(root);
        while (!level.empty()) {
            TreeNode* node = level.front();
            level.pop();
            swap(node -> left, node -> right);
            if (node -> left) level.push(node -> left);
            if (node -> right) level.push(node -> right);
        }
    }
};