Solution

• 中序遍历

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    TreeNode* Convert(TreeNode* pRootOfTree) {
        if (pRootOfTree == nullptr) return nullptr;
        traversal(pRootOfTree);
        return root;
    }
private:
    TreeNode* pre = nullptr, *root = nullptr;
    void traversal(TreeNode* pRoot) {
        if (pRoot) {
            traversal(pRoot->left);
            if (root == nullptr) root = pRoot;
            if (pre != nullptr) {
                pRoot->left = pre;
                pre->right = pRoot;
            }
            pre = pRoot;
            traversal(pRoot->right);
        }
    }
};