题目描述

递归和非递归

C++ 代码

blablabla
/**
 * 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>> findPath(TreeNode* root, int sum) {
        vector<vector<int>> res;
        vector<int> path;
        if(!root) return res;
        //dfs(res,path,root,sum);
        res = dfs(root,sum);
        return res;
    }
    //递归
    void dfs(vector<vector<int>> &res,vector<int>& path,TreeNode* r,int es){
        if(r) path.push_back(r->val);
        if(!r->left && !r->right){
            if(es == r->val) res.push_back(path);
        }
        if(r->left) dfs(res,path,r->left,es - r->val);
        if(r->right) dfs(res,path,r->right,es - r->val);
        path.pop_back();
    }
    //非递归
    vector<vector<int>> dfs(TreeNode* r,int sum){

        vector<vector<int>> res;
        vector<int> path;
        stack<TreeNode*> st;
        TreeNode* node = r;
        while(node || st.size()){
            while(node){ 
                st.push(node);
                path.push_back(node->val);
                sum -= node->val;
                node = node->left ? node->left : node->right;
            }
            node =  st.top();
            if(sum == 0 && !node->left && !node->right) res.push_back(path);
            st.pop();
            path.pop_back();
            sum += node->val;
            if(st.size() && st.top()->left == node) node = st.top()->right;
            else node = nullptr;
            }
            return res;
    }

};