【Leetcode】Path Sum II

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]
]

/**
* Definition for binary tree
* 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>> ret;
vector<int> path;
//这里注意判断空树，否则需要在下面的函数里面判断
if (root != nullptr) {
pathSum(root, sum, path, ret);
}
return ret;
}
private:
void pathSum(TreeNode *node, int target, vector<int> &path, vector<vector<int>> &ret) {
path.push_back(node->val);
if (node->left != nullptr) {
pathSum(node->left, target - node->val, path, ret);
}
if (node->right != nullptr) {
pathSum(node->right, target - node->val, path, ret);
}
if (node->left == nullptr && node->right == nullptr) {
if(node->val == target) {
ret.push_back(path);
}
}
path.pop_back();
}
};

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