LeetCode.22 反转二叉树

leetcode

题目

Invert a binary tree.
Example:
Input:
     4
   /   \
  2     7
 / \   / \
1   3 6   9
Output:
     4
   /   \
  7     2
 / \   / \
9   6 3   1

解答

简洁写法

/**
 * 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:
    TreeNode* invertTree_recursive(TreeNode* root) {
        if (root==NULL) return root;
        TreeNode* node = invertTree_recursive(root->left);
        root->left = invertTree_recursive(root->right);
        root->right = node;
        return root;
    }
};

带栈

// 带栈的写法
TreeNode* invertTree(TreeNode* root) {
    if (!root) return nullptr;
    stack<TreeNode*> s;
    s.push(root);
    while (!s.empty()) {
        auto p = s.top(); s.pop();
        std::swap(p->left, p->right);
        if (p->left) s.push(p->left);
        if (p->right) s.push(p->right);
    }
    return root;
}