二叉树：路径总和II，回溯优化的一些小收获

二叉树：路径总和II，回溯的一些个人理解

将target值在当前进行改变,回溯到改层是taget值未被改变：

		targetSum -= root->val;
        if(!root->left && !root->right && targetSum == 0)
        {
    
    
            result.push_back(path);
        }
        dfs(root->left, targetSum, path);
        dfs(root->right, targetSum, path);

或者把target作为参数传入函数中，调入下一层，回溯到时taget值依旧未被改变：

        if(!root->left && !root->right && targetSum == root->val)
        {
    
    
            result.push_back(path);
        }
        dfs(root->left, targetSum - root->val, path);
        dfs(root->right, targetSum - root->val, path);

class Solution {
    
    
public:
    vector<vector<int>> result;
    vector<vector<int>> pathSum(TreeNode* root, int targetSum) {
    
    
        if(root == NULL)
        return result;

        vector<int> path;
        dfs(root, targetSum, path);
        return result;
    }
    void dfs(TreeNode* root, int targetSum, vector<int>& path)
    {
    
    
        if(root == NULL)
        return;
        path.push_back(root->val);
        targetSum -= root->val;
        if(!root->left && !root->right && targetSum == 0)
        {
    
    
            result.push_back(path);
        }
        dfs(root->left, targetSum, path);
        dfs(root->right, targetSum, path);
        //回溯
        path.pop_back();
    }
};

总结：

对于优化代码不失为一个好办法！