[LeetCode]Path Sum II

题目解析:(链接)

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / 
            4   8
           /   / 
          11  13  4
         /      / 
        7    2  5   1

return

[
   [5,4,11,2],
   [5,8,4,5]
]

解题思路:

需要遍历所有路径

/**
 * 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<vector<int>> pathSum(TreeNode* root, int sum) {
        vector<vector<int>> result;
        vector<int> one_result;// 中间结果
        pathSum(root, result, sum, one_result);
        return result;
    }
private:
    void pathSum(TreeNode *root, vector<vector<int>> &result, int sum, vector<int> &one_result) {
        if (root == nullptr) return;
        
        one_result.push_back(root->val);
        if (root->left == nullptr && root->right == nullptr && sum == root->val) {//叶节点
            result.push_back(one_result);
        }
        pathSum(root->left, result, sum - root->val, one_result);
        pathSum(root->right, result, sum - root->val, one_result);
        
        one_result.pop_back();
    }
};