劍指 Offer 34. 二叉樹中和爲某一值的路徑

2020-07-02

1.題目描述

輸入一棵二叉樹和一個整數，打印出二叉樹中節點值的和爲輸入整數的所有路徑。從樹的根節點開始
往下一直到葉節點所經過的節點形成一條路徑。

2.題解

深度優先搜索：進行回溯的時候要恢復vector的狀態

3.代碼

/**
 * 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) {
        if (!root) return vector<vector<int>>(0);
        vector<int> tmp;
        tmp.push_back(root->val);
        dfs(root,tmp,root->val,sum);
        return res;
    }

    void dfs(TreeNode* node,vector<int> vec,int sumnow,int sum){
        if (!node->left&&!node->right){
            if (sumnow==sum){
                res.push_back(vec);
            }
            return ;
        }

        if (node->left){
            int tmp=node->left->val;
            vec.push_back(tmp);
            dfs(node->left,vec,sumnow+tmp,sum);
            vec.pop_back();
        }

        if (node->right){
            int tmp=node->right->val;
            vec.push_back(tmp);
            dfs(node->right,vec,sumnow+tmp,sum);
            vec.pop_back();
        }
    }

    vector<vector<int>> res; 
};