AM MS 878. Boundary of Binary Tree

Code(Language:C++) (Judger:ip-172-31-21-252)

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: a TreeNode
     * @return: a list of integer
     */
    void findLeaves(TreeNode *root, vector<int> &res){
        if(root == NULL){
            return; 
        }
        if(root->left == NULL && root->right == NULL){
            res.push_back(root->val); 
        }
        findLeaves(root->left, res);
        findLeaves(root->right, res);
        return; 
    } 
    vector<int> boundaryOfBinaryTree(TreeNode * root) {
        // write your code here
        //这种题就要拼思路了，有思路很简单。没思路现象，容易走错路。
        //1, 找leaves。
        //2, 找左边界。
        //3, 找右边界。
        vector<int> res; 
        if(root == NULL){
            return res; 
        }
        vector<int> lefts; 
        lefts.push_back(root->val);
        TreeNode *left = root->left; 
        if(left != NULL){
            while(!(left->left == NULL && left->right == NULL)){
                lefts.push_back(left->val);
                if(left->left){
                    left = left->left; 
                }
                else if(left->right){
                    left = left->right; 
                }
            }
        }
        vector<int> rights; 
        rights.push_back(root->val);
        TreeNode *right = root->right; 
        if(right != NULL){
            while(!(right->left == NULL && right->right == NULL)){
                rights.push_back(right->val);
                if(right->right){
                    right = right->right; 
                }
                else if(right->left){
                    right = right->left; 
                }
            }
        }
        vector<int> leaves; 
        findLeaves(root, leaves); 
        lefts.insert(lefts.end(), leaves.begin(), leaves.end()); 
        lefts.insert(lefts.end(), rights.rbegin(), rights.rend());
        lefts.pop_back();
        return lefts; 
    }
};