【LeetCode】226. Invert Binary Tree

Question

Invert a binary tree.

     4
   /   \   2     7
 / \   / \ 1   3 6   9

to

     4
   /   \   7     2
 / \   / \ 9   6 3   1

Code

BFS:

/** * 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(TreeNode* root) {
        if (root==NULL) return root;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            TreeNode* cur = q.front();
            q.pop();
            TreeNode* tmp = cur->left;
            cur->left = cur->right;
            cur->right = tmp;
            if (cur->left)  q.push(cur->left);
            if (cur->right) q.push(cur->right);
        }
        return root;
    }
};

There is a simple recursion solution:

TreeNode* invertTree(TreeNode* root) {
    if (root==NULL) return NULL;
    TreeNode* tmp = root->left;
    root->left = invertTree(root->right);
    root->right = invertTree(tmp);
    return root;
}

Note

Be careful for the NULL pointer！

When you use a pointer, please make sure that it is availble!