反轉二叉樹

尷尬了，昨天被問，忽然不知道咋搞。

 

二叉樹遍歷，前中後，是以root爲準的前中後

 

因此反轉二叉樹用後續遍歷就好

 

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

 

遞歸

struct TreeNode* invertTree(struct TreeNode* root)
{
    struct TreeNode *node;

    if (root == NULL)
        return root;

    node = invertTree(root->left);
    root->left = invertTree(root->right);
    root->right = node;
    return root;
}

 

非遞歸

struct TreeNode* invertTree(struct TreeNode *root)
{
    struct TreeNode *node, *tmp;
    Stack treeStack;

    if (root == NULL)
        return root;

    stack_init(&treeStack, NULL);

    stack_push(&treeStack, root);
    while (treeStack.size > 0)
    {
        stack_pop(&treeStack, &node);

        tmp = node->left;
        node->left = node->right;
        node->right = tmp;

        if (node->left)
            stack_push(&treeStack, node->left);
        if (node->right)
            stack_push(&treeStack, node->right);
    }
    stack_destory(&treeStack);

    return root;
}