【二叉树的递归】 - LeetCode

222. Count Complete Tree Nodes

最后一句递归。。。

226. Invert Binary Tree

二叉树的翻转

TreeNode* invertTree(TreeNode* root) {
        if (!root) return NULL;
        TreeNode *tmp = root->left;
        root->left = invertTree(root->right);
        root->right = invertTree(tmp);
        return root;
    }
230. Kth Smallest Element in a BST

 int kthSmallest(TreeNode* root, int k) {
        return kthSmallestDFS(root, k);
    }
    int kthSmallestDFS(TreeNode* root, int &k) {
        if (!root) return -1;
        int val = kthSmallestDFS(root->left, k);
        if (!k) return val;
        if (!--k) return root->val;
        return kthSmallestDFS(root->right, k);
    }
257. Binary Tree Paths