113 Path Sum II(樹的路徑之和爲一個常數）

113. Path Sum II

1 問題描述

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

給定一個二叉樹與整數sum，找出所有從根節點到葉結點的路徑,這些路徑上的節點值累加和爲sum

Note: A leaf is a node with no children.

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]
]

2 c++解答

class Solution{
public:
    vector<vector<int>> pathSum(TreeNode* root, int sum) {
        vector<vector<int>> result;
        vector<int> path;

        int current_value = 0;
        preorder(root, current_value, sum, path, result);
        return result;
    }
private:
    void preorder(TreeNode* node, int &path_value, int sum, vector<int> &path, vector<vector<int>> &result) {
        if(!node)
            return;
        path_value += node->val;
        path.push_back(node->val);
        if(!node->left && !node->right && path_value == sum)
            result.push_back(path);

        preorder(node->left, path_value, sum, path, result);
        preorder(node->right, path_value, sum, path, result);

        path_value -= node->val;
        path.pop_back();
    }
};