[leetcode] Path sum路径之和

要求
给定树，与路径和，判断是否存在从跟到叶子之和为给定值的路径。比如下图中，给定路径之和为22，存在路径<5,4,11,2>，因此返回true;否则返回false.
              5
             / 
            4   8
           /   / 
          11  13  4
         /        
        7    2      5
思路
递归，从跟到叶子判断，如果在叶子处剩下的给定值恰好为给定值，那么返回ture.
参考代码

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool hasPathSum(TreeNode *root, int sum) {
        if (root == NULL)
            return false;
        else if (root != NULL && root->left == NULL && root->right == NULL)
        {
            if (sum == root->val)
                return true;
            else
                return false;
        }
        else
            return hasPathSum(root->left, sum-root->val) || hasPathSum(root->right, sum-root->val);
    }
};

扩展

求出所有符合条件的路径。例如，上题中返回<<5, 4, 11, 2>, <5, 8, 4, 5>>

参考代码

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void addPath(TreeNode *root, int sum, vector<int> tmp, vector<vector<int> > &rev)
    {
        if (root != NULL && root->left == NULL && root->right == NULL && root->val == sum)
        {
            tmp.push_back(root->val);
            rev.push_back(tmp);
            tmp.pop_back();
        }
        if (root->left != NULL)
        {
            tmp.push_back(root->val);
            addPath(root->left, sum - root->val, tmp, rev);
            tmp.pop_back();
        }
        if (root->right != NULL)
        {
            tmp.push_back(root->val);
            addPath(root->right, sum - root->val, tmp, rev);
            tmp.pop_back();
        }
    }
    vector<vector<int> > pathSum(TreeNode *root, int sum) {
        vector<vector<int> > rev;
        if (root == NULL)
            return rev;
    
        vector<int> tmp;

        addPath(root, sum, tmp, rev);
        return rev;
    }
};