binary tree path

http://www.lintcode.com/en/problem/binary-tree-paths/

https://leetcode.com/problems/binary-tree-paths/

code

Leetcode 2016/12/15

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root == NULL || p == NULL || q == NULL)
        {
            return NULL;
        }

        if(p == root || q == root)
        {
            return root;
        }

        TreeNode* left = lowestCommonAncestor(root->left, p, q);
        TreeNode* right = lowestCommonAncestor(root->right, p, q);

        if(left != NULL && right != NULL)
        {
            return root;
        }

        if(left != NULL)
        {
            return left;
        }

        if(right != NULL)
        {
            return right;
        }

        return NULL;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string> vec;
        if(root == NULL)
        {
            return vec;
        }
        string cur;
        dfs(vec, cur, root);
        return vec;
    }

    void dfs(vector<string>& vec, string& cur, TreeNode* root)
    {
        if(root == NULL)
        {
            return ;
        }
        string original = cur;
        cur += to_string(root->val) + "->";

        if(root->left == NULL && root->right == NULL)
        {
            cur.pop_back();
            cur.pop_back();
            vec.push_back(cur);
            cur = original;
            return;
        }

        dfs(vec, cur, root->left);
        dfs(vec, cur, root->right);
        cur = original;
    }
};

/*
 * 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 the root of the binary tree
     * @return all root-to-leaf paths
     */

    void dfs(vector<string>& path, string& cur, TreeNode* root)
    {
        if(root == NULL)
        {
            return ;
        }

        string old = cur;
        cur += "->";
        cur += to_string(root->val);

        // 坑2 leaf的判断条件

        if(root->left == NULL && root->right == NULL)
        {
            path.push_back(cur);
        }
        else
        {
            dfs(path, cur, root->left);
            dfs(path, cur, root->right);
        }

        // 坑3 要回退

        cur = old;

    }

    vector<string> binaryTreePaths(TreeNode* root) {
        // Write your code here
        vector<string> vec;
        if(root == NULL)
        {
            return vec;
        }

        // 坑1：single node tree

        string cur = to_string(root->val);
        if(root->left == NULL && root->right == NULL)
        {
            vec.push_back(cur);
            return vec;
        }
        dfs(vec, cur, root->left);
        dfs(vec, cur, root->right);
        return vec;
    }
};