LeetCode: 113. Path Sum II

题目描述

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

深度搜索遍历所有的路径，记录和为 sum 的路径。

AC 代码

/** * 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 {
private:
    void pathSumRef(TreeNode* root, int sum, vector<int>& path, vector<vector<int>>& paths)
    {
        if(root == nullptr) return;
        if(root->left == nullptr && root->right == nullptr && sum == root->val)
        {
            path.push_back(root->val);
            paths.push_back(path);
            path.pop_back();
        }
        else if(root->left == nullptr && root->right == nullptr)
        {
            return;
        }
        else
        {
            path.push_back(root->val);
            pathSumRef(root->left, sum - root->val, path, paths);
            pathSumRef(root->right, sum - root->val, path, paths);
            path.pop_back();
        }
    }
public:
    vector<vector<int>> pathSum(TreeNode* root, int sum) {
        if(root == nullptr) return {};
        vector<vector<int>> paths;
        vector<int> path;

        pathSumRef(root, sum, path, paths);

        return paths;
    }
};