Easy-20

leetcode   226. Invert Binary Tree

Invert a binary tree.

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

to

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

AC;

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

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

tips:开始准备想着遍历把值取出来，然后逆序，再遍历放回去。后来又发现只要遍历一次，遍历过程中交换左右子树即可。想出这个方法，对于菜鸟的我来说，很激动！~